AQUARIUM LIGHTING INFORMATION GUIDE | Reef Planted | PAR PUR/PAS
Complete Facts & Information To Help In Understanding Kelvin, Nanometers, PAR.
Written with professional experience & research since 1979.
(1) Aquarium Lighting Factors
(2) Kelvin Rating
(3) Nanometer Range (Spectrum)
(5) PAR (Photosynthetically Active Radiation)
(6) Measuring PAR
(7) Quality of Light (PUR, RQE, PAS)
|(12) Aquarium Light Type||
(15) Light on time & change
(16) Lamp placement
(17) Light Penetration
(18) Specimen Placement
(19) BASIC LIGHTING SET UP SUGGESTIONS
(21) PDF of this Article
AQUARIUM LIGHTING, Information including Factors, Types, & Use
By Carl Strohmeyer- PAMR 35+ years experience
Video version of the first section of this article:
Aquarium Lighting 2018 | Kelvin, PAR, Watts and More
When choosing your aquarium lighting, there's MUCH MORE to consider than just "WATTS PER GALLON". Back in the days of buying your fluorescent cool white or warm white T12 or T8 lights (often even at hardware stores), this 'rule' was quite useful since we were more comparing "apples to apples". Often this would range from 3 to as much as 5 watts per gallon, but this now is quite outdated for most modern lights.
In fact, the 'Watts Per Gallon' should only be used within the same type & make depending upon what is kept. This is due to the variety of available modern lights with varying lumens per watt, different wavelengths, focused lumens, PAR, PUR, PAS, & RQE.
As an example, a high PAR/PUR LED only need about 4% to 15% of typical aquarium T8 or T12 lamps.
Now we generally will start with the the PAR for what we intend to utilize our lights for (although many will often use higher PAR readings than necessary).
Even then with the many LEDs available, we need to look at input energy versus output energy since often the same input in watts (joules of energy) can have a different output in PAR due to wasted heat energy in drivers, controllers, fans, etc. In fact these efficiencies just within LED light can vary greatly with some as efficient as .08 watt per mm of PAR (one model of AAP AquaRay) & as inefficient as 2.7 watt per mm of PAR (a Beamsworks LED).
Then we get to the QUALITY of the light output as per the application & this too can vary, even with the same PAR output (photons of light), meaning one light with the same PAR reading can be superior over another.
There are other factors I will cover in this article affecting lighting for your aquarium.
For example: You cannot compare the output of a 150 watt Metal Halide to a 150 watt outdoor floodlight. Nor an 85 watt standard incandescent to an 85 Watt 6400 K SHO Bulb.
What I am trying to say is often it comes down to comparing apples to oranges.
If you are TRULY interested in the "BEST AQUARIUM LIGHTING", Please read this ENTIRE article to understand ALL parameters necessary for your aquarium light determination.
Products described in this article are primarily used because I & other professionals I trust have many years of real world experience with them.
No one should come away with a feeling of obligation to purchase these products, rather a greater understanding of aquarium lighting & their applications.
This said, I do not try to appeal to the "cool kids club" of lighting too. My recommendations are based on my experience & research, not being bought out. Many of today's modern lights will work on your planted or reef tank, but often you will find at much lower efficiencies, even though capable. So if you are looking for the best best on science & experience, please read on, if you want to be popular just go with what popular forums recommend.
Lights as they apply to aquarium use have evolved/changed considerable since I have been in the hobby & professionally employed in aquarium set-up & design.
We often used "hardware store" warm white T12 fluorescent lights, just in larger "quantities" to make up for the poor "quality" of light, even while planted freshwater could be kept, not so with ANY photosynthetic reef life.
Early on lights such as the "Aquarilux" came out which still was heavier on the "warm" colors, it also had more blue.
Later the Trichromatics & Triton lamps came out with spectrums focusing on the daylight 6500 Kelvin temperature, these made growing planted aquariums easier with less lights to do the same job as earlier lights.
We also had actinic blue lights become available, these mixed with other lights made it possible in the beginning to keep some photosynthetic reef life, although initially these did not thrive. Later T6 & T5 advancements along with Metal Halide lights allowed us to not only keep delicate photosynthetic reef life, but for this life to thrive.
We now have T2, SHO, & LEDs of which the later have lowered considerably the input energy for the quantity of output energy of light that we need for our aquarium keeping applications.
This overview is just a brief explanation of aquarium lighting.
It is important to note that Aquarium Lighting is a complex subject, & this article has both more in depth information as well as some basics.
However this is a subject that, by reading one section, will yield incomplete information. For this reason I recommend reading the whole article (as well as links provided) for a more thorough understanding (it may take more than one reading)
I should also note that while I have years of hands on professional experience (since 1978), this is a fast evolving subject of aquarium keeping requiring my constant research & consulting with many others for their scientific expertise/experience. The result is constant changes/updates to this article.
For cynical readers of this article who claim I have a bias; obviously I do, but then this is based on much research & use.
WHY WOULD I RECOMMEND ANY PRODUCT THAT RESEARCH & EXPERIENCE SHOWS TO BE INFERIOR TO ANOTHER?
In fact many of the Lighting Products I recommend and admittedly sell were not even available in the earlier drafts of this article since it was first written in the 1990s & added to the Internet in 2005, It was my research, consulting, & experience that led me to the products I now recommend!!
As a BRIEF generalization, we are first concerned with INPUT energy, then OUTPUT energy. This can be further simplistically broken down into these 6 considerations:
• PAR (output energy)
• PUR/Useful Light Energy/Quality of Light as per application (output energy). This is an important factor often missed by aquarium keepers
• Lumens per watt (input/output energy)
• Lumen focus, as well as restrike (output energy)
• Wattage used (input energy)
• Energy lost as heat via fans, transformers, drivers, method of controlling, etc. (input energy)
Finally, it is still worth noting that even our best man made lighting is still far inferior to sunlight. So short of placing our aquarium outdoors, all we can do is attempt to emulate at least the most useful aspects of sunlight energy that we can.HERE ARE THE IMPORTANT FACTORS IN DEPTH;
What is meant by Kelvin Temperature of Lights is not the classic interpretation of the meaning of Kelvin.
Kelvin is used in the lighting industry to define the Color temperature of a bulb.
Higher color temperature lamps above 5500 K are "cool" (green–blue) colors, & lower color temperature lamps below 3000 K are "warm" (yellow–red) colors.
However, Kelvin is ONLY AN INDICATOR of what the light spectrum in nanometers MIGHT be, not an exact prediction, so be careful about comparing light output solely by Kelvin (actual spectrums & PUR are better measurements)Kelvins, as applied to color temperature of lights, are derived from the actual temperature of a black body radiator. Which is the concept of color temperature based on the relationship between the temperature & radiation emitted by a theoretical standardized material and termed a "black body radiator". This is where the "classic" definition of Kelvin, & how it relates to light, come together. Hypothetically, at cessation of all molecular motion (the black body state of this hypothetical radiator), the temperature is described as being at absolute zero or 0 Kelvin, which is equal to -273 degrees Celsius.
An incandescent filament is very dark, and approaches being a black body radiator, so the actual temperature of an incandescent filament is somewhat close to its color temperature in Kelvins.
Incandescent lamps tend to have a color temperature around 3200 K, but this is true only if they are operating with full voltage. When a lamp is dimmed below its full potential, its filament is not as hot, and it produces less light. The reduced temperature of the filament also reduces the color temperature downward. An incandescent light dimmed to 10% is considerably more red in color than one at 100%.
Another consideration of the color temperature as applied to lights; color temperature does not take into consideration the spectral distribution of a visible light source. In cases where a light source, such as a fluorescent lamp, arc-discharge burner, laser, or gas lamp, do not have a spectral distribution similar to that of a black body radiator.
A few generalized notes about Kelvin:
An example here would include using warm white & blue fluorescent lights or LED emitters could also be used): If eleven warm white lights or emitters (3000k) along with one blue light/emitter at 50000k, one would multiply 11 x 3000 + 1 x 50000 = 83000 ÷ 12 (total lights or emitters) = 6916k. In other words you can obtain an overall 6900 kelvin rating with this combination. Frankly this would provide a very inefficient/poor way to reach a good daylight kelvin since your lights would be very heavy in warm yellows, reds, & some greens, with a less than optimal photosynthetic action spectrum (PAS).
This is why often comparing one 6500K lamp to another can often be "apples to oranges" as for necessary useful light energy (PUR) needed by plants or corals. Another reason why Kelvin ratings are often poor methods to rate modern aquarium lights.
HOWEVER, be wary of comparisons of so called 6500K lights which are clearly NOT all 6500K lights to anyone with any aquarium lighting history experience!
While variations in spectrums, and even how the color appears to us, is to be expected as for reasons given, they are not this dramatic also for the reasons already given.
In this picture, the two in the top are misleadingly flagged as 6500K, when in fact the pink one is clearly an Aquarilux knock off. The Aquarilux is a popular lamp used to provide color for aquariums back in the 1970s, 80s, & into the 90s. It was NOT marketed as a 6500K or planted aquarium lamp and did NOT perform as well as those that were such as the Trichromatic or Tritons!
What Kelvin Rating for Plants & Corals;
Here are some observations made by me and others in the professional aquarium maintenance community, some of these are simple observations, while others were based on more controlled tests. Please understand that these are still generalizations!
The Kelvin rating is another area of comparing apples to apples in lights. The above content is a simplified explanation of Kelvin as it applies to lights.
This does not mean that a certain Kelvin bulb is necessarily "better" as factors such as "lumens per watt", watts of energy used, focused lumens, PAR, & especially PUR MUST be considered as well.
micro.magnet.fsu.edu/primer/java/colortemperature Color Temperature in a Virtual Radiator- This is an interesting resource worth checking out.
Mixing Primary Colors
This is a fun/interesting online tool!
A nanometer scale is used to measure the wave length of light energy from cosmic rays to radio waves.
An actinic bulb will have a Nanometer spike at about 420nm, a UVC bulb about 265nm, & a daylight bulb about multiple spikes from 400 to 700nm.
The difference in the wavelength determines how the wave affects its surroundings. It is this wavelength difference that allows short-wave x-ray to pass through walls, while longer-wave visible light cannot pass though the same material; short-wave ultraviolet & x-ray can destroy DNA in living microorganisms & breakdown organic material while visible light will not. All light energy is measured on a "nanometer" (nm) scale. Nanometer means one-billionth of a meter.
This applies to aquariums when we consider the light spectrum & how it applies to our aquariums individual needs: Red light is the first to be filtered out & can only penetrate a short distance. As light waves penetrate deeper into the water, orange & yellow are lost next. Of all the colors of the spectrum blue light penetrates the deepest. Corals need intense equatorial UVA (actinic) as well as other aspects of PAR.
Most higher plants need a balanced PAR light range which includes the blue & two red spikes required for photosynthesis (see section about PAR, PAS & PUR).
The Nanometer scale & Kelvin temperatures come together when applied to aquarium lighting this way; Natural sunlight on a clear day registers at 5500- 6500 Kelvin degrees. Kelvin temperatures less than 5500K become more red & yellow & the higher the Kelvin temperature the more blue the light is.
Most photosynthetic marine invertebrates should be kept with lamps of a daylight Kelvin temperature from 6400-14,000 K (higher Kelvin with deeper specimen placement, not necessarily tank depth). 20,000K daylight lamps can also be used for deeper tanks (over 22 inches) and/or supplementation with more blue lights (400nm- 490nm).
Photosynthetic invertebrates (many corals, anemones, clams, nudibranch, etc.) also need more blue (400-490nm) than "higher" plants especially as tanks increase in depth, such as the 465-485 blue spectrum. Not only is blue/actinic lighting beneficial to photosynthetic invertebrates, it is also aesthetically pleasing to the eye and the 420 nm blue in particular brings out the colors of many corals/clams.
Osram Oslon now has a "patent pending" LED emitter (the NP Blue) that is the first 'blue' emitter SPECIFICALLY designed for the full PAR spectrum required by marine photosynthetic invertebrates (see LED Section for more)
It is noteworthy that Fluorescent and even more so incandescent lights produce a lot of yellow & green nanometer light, which research indicates is mostly wasted energy in terms of the needs or freshwater plants & SPS Corals. This is where an LED Aquarium Light or Metal Halide excel as there is often less of the less efficient yellow/green light.
See the picture to the left that shows a T8 5500 daylight aquarium light that is commonly sold, this graph clearly shows the less efficient green/yellow energy as well as the incorrect spike in orange rather than the correct PAR spike in red 630+ nm
It is also noteworthy that many "terrestrial plant lights" as well as many aquarium plant lights (often of lower in kelvin temperature) have more "red nanometer spikes" than higher kelvin 6500k, 10,000k & higher lamps.
The problem with these lights is that while all plants utilizing photosynthesis require the same essential ABCs of PAR (see the PAR section), the facts of light energy penetrating water requires higher kelvin (6500k +) be added to provide maximum PUR (see Useful light energy/PUR section). Aquatic Plants and corals have adapted/evolved to the natural light energy at certain depth of water and the misguided attempt to adapt these terrestrial plant lights is not going to be 100% effective as a light with more water penetrating blue & slightly lower red nm energy.
A measure of the intensity of light (referred to the photometry of light), one lux is equal to one lumen per square meter. This is another area of comparing apples to apples in lights, not just watts.
It is noteworthy that a LUX Reading ONLY reports light intensity to which the HUMAN EYE is most sensitive (green light)
While this measurement only includes light visible by humans, this can still be a useful tool for freshwater plants & most corals in marine reef aquariums.
When the Lux is not enough, the zooxanthellae (inside of corals tissues) do not create plentiful oxygen.
The minimum light intensity should be no less than 3,000-lux when it reaches the deepest part of the aquarium. You can over light your coral to a light saturation point (quite hard in my experience, but this should be noted), maximum Lux should be no more than 100,000 to 120,000.
By comparison Lux in tropical reefs has been measured to be between 110,000 and 120,000 Lux at the surface of the reef and 20,000-25,000 Lux one meter below the surface.
PAR is an important and accepted starting point to estimate light energy for our photosynthetic aquarium keeping needs. We measure PAR via µMolm which is a unit of measure (more about measurement later).
While PAR is important, it is often incorrectly used as the only measure by both marine & freshwater plant keeping aquarists, especially by many marketing pros and popular video channels when PUR/PAS/RQE is ALSO important and should be considered.
PAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers that is generally accepted as needed by plants & symbiotic zooanthellic algae for photosynthesis (Zooxanthellae are single-celled algae that live in the tissues of animals such as corals, clams, & anemones).
It is also noteworthy that while outside of the accepted PAR, a study using infrared (IR) LEDs of 880 nm & 935 nm on etiolated oat seedlings showed leaf emergence, so these parameters may someday need better defining (See Reference at the end of article).
The graph above is only meant to show the boundaries of currently accepted PAR light and the relative quantum efficiency (RQE) therein
UVA to 550 nm contains the absorption bandwidth of chlorophylls a, c˛, and peridinin (the light-harvesting carotenoid, a pigment related to chlorophyll). The photons of light energy within these spectrums are more energetic and by themselves tend to provide more plant growth
620-720nm is the red absorption bandwidth of chlorophylls a and c˛.
Photons at shorter wavelengths (UVC) tend to be so energetic that they can be damaging to cells and tissues; fortunately they are mostly filtered out by the ozone layer in the stratosphere. Green light occupies the middle spectrum and is partly why chlorophyll is green due to the reflective properties (30%).
Lights that produce light energy under 500nm will produce a lower PAR reading for a given energy input (wattage), not because less energy is emitted, rather because most PAR meters are less accurate below 500nm.
Lights that occupy mostly the middle spectrum (500-600/ green-yellow) such as "Warm White (2700- 3500K ) will produce LESS EFFICIENT PAR, in other words less PUR (which is discussed in more depth in the next section). This does not mean that these spectrums are totally useless either as noted by cited updated resources within this article such as Oregon State Univ.
*Phototropic response; having a tendency to move in response to light. Basically this is the Chlorophyll containing plant or algae "moving" to respond to a positive light source to begin the process of photosynthesis (initial growth of plants, zooxanthellae, etc.).
*Photosynthetic response; During this time, the molecules needed for photosynthesis gradually reach operating levels which begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls.
*Chlorophyll synthesis; occurring in chloroplasts, this is the chemical reactions and pathways by the plant hormone cytokinin soon after exposure to the correct Nanometers wave length , that traps the energy of sunlight for photosynthesis and exists in several forms, the most abundant being Chlorophyll A.
This results in continued growth of a plant, algae, zooxanthellae and the ability to "feed" & propagate. Without this aspect of PAR, zooxanthellae & plants cannot properly "feed" propagate resulting is stunted freshwater plant growth, and eventually poor coral health in reef tanks.
This is also known as the Photosynthetic Action Spectrum (PAS).
*Chlorophyll A; A type of chlorophyll that is the most common photosynthetic organisms predominant in all higher plants, red & green algae higher plants, red & green algae. It is best at absorbing wavelength in the 400-450 nm & 650-700 nm
*Chlorophyll B; The chlorophyll that occurs only in plants & green algae. It functions as a light harvesting chlorophyll pigment that pass on the light excitation to chlorophyll a. It absorbs well at wavelength of 450-500 nm & 600-650 nm
Since many photosynthetic organisms live where light in higher spectrums of PAS such as 600nm & higher penetrate less if at all (in particular algae, zooxanthellae, & cynaobacteria), many have adapted to ways to still harvest this light energy.
These organisms use Phycobilisomes which are light harvesting antennae of photosystem II (Chlorophyll synthesis in the Photosynthic Action Spectrum-PAS).
For this reason it is noteworthy that while any light within the PAR range can be used, providing light energy outside certain proven/evolved aspects of PAS can result in poor growth or allowing of less desirable algae to out compete plants or coral we are attempting to cultivate. This why it is a FACT that while certain lights may keep photosynthetic life, less than optimum spectrums found in many of the inferior lights will either produce lessor results and/or require more input light energy for the same results as say a high PAS & PUR light such as the AAP AquaRay.
Reference: Aquarium Algae Control; BBA
Further PAR Information;
As a light energy penetrates deeper through water, these need to move slightly "left" (lower) on the nanometer graph so as to allow for optimum use of PAR (in other words Photosynthetically useful radiation; please see the PUR/PAS section).
This can vary with light type though as not all so-called daylight bulbs are the same, see the PUR & PAS section of this article.
Although Kelvins (as well as LUX conversions using questionable LUX to PAR conversion factors) are ways of getting rough estimates of PAR, only a Specific PAR Meter (also called Quantum Light Meters) which uses a standardized unit of measure can give you the best measurement of this aspect of determining your tanks lighting requirements (both at the surface and under the surface)
Currently accepted numbers measured as µMol•m˛•sec (also referred to as micro mols, mm, or mmol) are 50 mmol for most plants or corals such as Nemezophyllia, while Acropora can require higher PAR outputs.> Keep in mind though, that if one light is using a shotgun approach to achieving a high PAR reading with wasted energy in spectrums outside known needed PUR & PAS, you may need a higher PAR reading, while the reverse may be true of a very efficient PUR light that might achieve excellent results at 50 mm compared to the "shotgun" light that might require 200 mm for the same corals or plants to achieve good results.
It is noteworthy that a study of a Coral Farm in Bali showed no more than 200 PAR from noontime tropical sunlight at the depth the acropora were being grown!
Reference: PUR, PAS, RQE, PAR in Aquarium Lighting
HOWEVER, keep in mind that a PAR Meter is NOT accurate in important light energy spikes WITHIN the 400 to 700 nanometer range, so while one light might measure a higher PAR mmol reading, another light might be still superior due to the more important PUR & PAS output.
This is where I have found the use of a PAR Meter SOLELY to determine light efficiency over rated.
As an example understanding PAR numbers, just within the SAME BRAND of emitters & LED lights; using the same energy input of 12 joules (watts) at 400mm we know the measured µMolm of the CRee XT-E Fiji Blue is 38 µMolm while the CRee XB-D 6500K Natural daylight is 61 µMolm
BOTH use the same amount of energy, and in fact the Fiji Blue is actually deeper penetrating, YET the Natural Daylight produces much more light energy as expressed in PAR/µMolm!
Looked at another way, if you were to increase the number of emitters of the XT-E Fiji Blue to equal the XB-D 6500K (approximately 37%), would you now suddenly be able to say this light would work perfectly over one's high light planted aquarium?
Of course not! Even if you could, this also makes the point of how one more similar LED or other light can have a higher useful light energy output (PUR) for the less input of energy as expressed in watts/joules.
This is not to say the XT-E Fiji Blue is poor emitter, only that one needs to take PAR/µMolm measurements in context & that you cannot compare apples to oranges. One could also make similar comparisons with cool white T8 versus 6500K LEDs or even one 6500K light to another 6500K light.
Some organisms, such as Cyanobacteria, purple bacteria & Heliobacteria, can make use of the unusable light discarded by the plant kingdom, in this case, light outside the PUR range required by plants, which is why Cyanobacteria thrive in lighting conditions that include more yellow light energy.
Reference: Red Slime Cyanobacteria
*Photosynthetically Active Radiation
Many recent studies have shown the importance of full spectrum lighting as it relates to health in humans & animals, can be extrapolated to fish as well for a disease prevention which is why good lighting should not be restricted to Reef Marine or Planted Freshwater Aquariums, but to fish only salt or freshwater tanks as well.
Aquarium Disease Prevention
PUR (Photosynthetically Usable Radiation) is something aquarium keepers should concern themselves with along with PAR in providing correct lighting since it describes the quality of light photons as per application.
PUR cannot be dismissed as some lighting experts have attempted to do based on their short time in the professional aquarium keeping industry, as we have already clearly established (as per the Overview section) that we found that once more precisely tuned spectrum fluorescent lights became available, we could grow aquarium plants more efficiently and with some advancements, this made the difference of not keeping photosynthetic marine organisms at all!! I should note that some of these advancements were comparing apples to apples; T12 to T12 such as a warm white to a Trichromatic or an actinic (which rules out lumens per watt and other measurements and leaves the FACT of PUR).
Another term is Photosynthetic Action Spectrum (PAS). I should point out that while the terms PAS & PUR have a lot in common, there is a difference in that PAS is most simply stated as the spectrum where "chlorophyll is much more efficient at using the red & blue spectrums of light to carry out photosynthesis. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colors red & blue."
Reference: Action spectrum; Wikipedia.
While PUR also encompasses this too it also can simply refer to all light spectrums within PAR with emphasis on the more efficient spectrums rather than the less efficient spectrums such as yellow & green. Or stated another way, the portion of PAR, which is more efficiently absorbed by plants & zooxanthellae photopigments thereby stimulating photosynthesis. We can state PUR one more way, where as PAR is the most important quantity of light, "PUR is the quality of light as per application".
The picture above depicts both full solar radiation that reaches the earth as well as how a few different man-made light sources fit into the visible/PAR aspect of this spectrum.
What is noteworthy is how much radiation falls outside the PAR, in particular the longer frequency wave lengths going into radio waves. There is much that we also do not know, since photosynthetic plants, zooanthellic algae, etc. might also be using radiant energy we do not know about. What we do know is that since UVC is not reaching the earth's surface and that even UVB only reaches in small amounts (if at all during certain times of the day and seasons), that it is likely this is mostly useless for our application.
It is therefore reasonable to attempt to duplicate the sun's radiant energy that reaches the earth's surface which the Daylight (6500K) LED emitter is reasonably close when compared to the other light sources. Obviously once water is thrown into the equation, more blue is going to be needed, as well we must take into account the 20-30% reflection of green light.
There has been a lot of confusion about this subject, especially when considering LED lights, as many sellers and aquarium keeping personalities with little background will hype high PAR values while ignoring PUR. Often terminology is confused or "Red Herring" type arguments are made to confuse the subject, but regardless of what you call it by, we have had a general knowledge of PUR, RQE, & PAS for some time.
Many people will think PUR is good in theory, but think it cannot be applied to every single species we are trying to grow under water. While we don't know every species and it's preferred nm of light prefers, we do know the light, which triggers photosynthesis in an organism as well as efficiencies based on real world tests.
Another misapplication that is often applied in certain aquarium keeping circles where they have apparently not done their research into the history of aquarium lighting as per PUR is to compare a high PUR light to a lower PUR light of much higher input wattage.
As an example, I have seen the Ocean Revive LED of 120 watts that is a larger fixture with a larger footprint compared to an AAP AquaRay NP 2000 Reef White that only has 30 watts, then state the AquaRay is under powered. However if you match input wattage, you will in fact get much more raw light as well as useful light if four of the AquaRays were to be compared (which in reality, you would likely not need this many to do the job).
A little history: since I have been in the industry on the research and aquarium system design side since 1978. I have called this subject "useful light energy" since at least 1985. Then, I read elsewhere that the more scientific terms of PUR, RQE, & PAS. This explained it well, based on feedback from clients and others in the industry despite others attack upon this term. Frankly a new term that I have heard thrown around that I think is less vague would be "Quality of Light per Application".
The ability of newer technology lights to pin point the exact nanometer spectrums needed for PUR in output results in much less wasted energy and allows for a light of considerably lower wattage to actually out produce another light of higher wattage.
Even the best of fluorescent lights that are a Kelvin temperature of 6500K, use a percentage of their light energy in the yellow & green light spectrum which is much less efficient for aquarium plants or corals, although some green light can actually improve growth when less than 24% of overall light spectrum (Reference: Ref. 1).
The picture to the left displays how quality of light or "useful light energy" plays out in real world tests.
Since it is well established that a photon is a photon and it is the quantity that certainly makes the most difference (PAR is quantity), we still cannot ignore the quality of the photon of which the only difference of a photon is the wavelength and frequency (energy).
The first graph shows how red, green, & red light growth based on weight of lettuce. It is clear from the picture that the green light is only 50% of the efficiency of red & only 20% of the efficiency of blue.
The second photo demonstrates how one light (the Metal Halide) has much more input energy (joules) and even after the known massive loss of input energy, it still has more photons (expressed as lumens here) than the 6500K Generic Gro Light LED, yet the outcome of growth is dramatic!
Both these examples demonstrate how photosynthesis and plant growth obviously favors photons of specific frequencies!
For a further explanation, please read this article:
Real World Application of RQE, PAR. PUR, PAS, & Photons
The picture below shows a spectrograph of two 6500K aquarium lights. One is an AAP AquaRay GroBeam and the other is a 6500 Aquarium CFL. The LED is rated at 12 watts while the CFL is 13 watts.
While similar, it is clear to see the LED has more blue and a lower blue NM (fuller blue spectrum) amount as well as more red, less green, and the same yellow.
The point this makes/demonstrates is that while both lights are rated as 6500K, they are still not the same in their light energy output. Even among LED lights we can have differences of spectrographs depending upon emitters used.
Think about how mixing all paint colors will produce black, while the mixing of all light energy produces white. We as humans may notice this to some degree, however we do not have the ability to pick out particular colors such as a honey bee can. As well, photosynthetic aquatic life also has differing abilities to pick out the needed light energy for life processes and even though the PAR readings may be equal, the light energy that provides this overall PAR or kelvin "color" is NOT.
A Couple more points to better explain the concepts of PUR, "Useful Light Energy", or "Quality of light per application".
For further reading about PUR:
This is another concept to consider that we do not know all the "mechanisms" that drive it.
Basically photoinhibition is the damage to the light harvesting reactions of the photosynthetic capacity of a vascular plant, algae, or cyanobacterium by excess light energy trapped by the chloroplast.
This process can occur in in all organisms capable of oxygenic photosynthesis. In both plants & cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, although it has been demonstrated the red light can cause photoinhibition as well.
One of the implications for us as aquarium keepers is this process can often be the result of new light systems until our plants, photosynthetic corals, etc. adapt to the new light.
The other implication is while we may still see good growth of our plants or coral, we often are "over driving" light to where not only are you wasting input energy for unnecessary PAR number the growth is not as good as it could be. This is common now with many popular well marketed LEDS such as the SB Reef Light.
This graph demonstrates maximum photosynthesis in the zooxanthellae in this Porites stony coral was achieved at about 200 µmol·m˛·sec. At 350 µmol·m˛·sec the rate of photosynthesis was about that seen at 75 µmol·m˛·sec!
The Myth of Corals Requiring Unlimited Amounts of Light
The international unit of luminous flux or quantity of light used as a measure of the total amount of visible light emitted. The higher the lumens, the "brighter" or more "intense" the light looks to the human eye. You can figure lumens per watt by dividing the lumens your lamp lists by the wattage the fixture lists.
Knowing your lumens per watt is just one more small piece of the "aquarium lighting puzzle".
For example a T12 light that is rated at 20 watts with a total lumen output of 800 lumens has a lumen per watt output of 40. While a 13 watt T2 bulb rated at 950 lumens has a lumen output of 73 lumens per watt. This is a clear example that the watts per gallon rule is severely flawed, as the 13 watt T2 (or two of these) is clearly the better choice for a 15 gallon planted aquarium and this does not even take into consideration the PAR/PUR which is also important for plants/corals.
It is also noteworthy that even the lumen output can be deceiving when considering aquarium lights.
The best LED Lights are a good example of this as these newer technology lights have extremely focused light energy with little essential light energy lost (such as by Restrike), unlike almost every other type of aquarium light currently available.
With this focused energy a "high end" LED often requires half the lumens (or often even less) to provide essential light energy to plants, corals, etc. The newer generation LED lights have considerable less loss of lumens at 20 inches than a CFL light (as per tests that show 166% more lumens for the same wattage LED as compared to a common CFL of equal wattage).
Caution as to using Lumens as a useful measurement of Light Output:
While lumens are a important useful measurement for standard household light bulb comparison, it is only a part of the equation for aquarium use, especially when this measurement is applied to new technology lights employed by aquarium keepers (such as LEDs).
As an example of just one aspect where the lumen measurement falls short is when Kelvin is considered; a cool white lamp emitting 1000 lumens at a color temperature of 5,500K will not emit as much PUR as a lamp emitting 1000 lumens at 6,500K.
More over, when compared to "Useful Light Energy" (PUR), Lumen output falls well short as useful comparison of light output.
This said, I am not saying Lumen output and focused lumens are useless, as these parameters are a piece of the light parameter "pie", but often it is overrated and these parameters should only be taken as a part and a small part at that when compared to PAR & PUR.
Watts equal one joule of energy per second. For us, it's a measurement of how much energy our light fixture is using NOT OF LIGHT OUTPUT!
This is why the old rule: "3-5 watts per gallon" can be deceiving, and this rule is only a starting point at best of late. This archaic rule was more accurate when all that was used were T12/T8 lamps which is what this rule is based on.
Keeping this in mind the average T12 has a lumens per watt rating of 40, which means you would need half as many watts of a bulb that produces 80 lumens per watt (assuming PUR & other aspects are equal).
The term "watts per gallon" is getting more archaic with the newer T-5, CFL, the SHO, & especially the new reef compatible LED lights.
Even within LED Lights, one 30 watt LED is not equal to another 30 watt LED.
An example, you cannot compare a 30 Watt AAP/TMC Reef White to a 130 watt EcoTech Radion. However if you were to use an equal wattage of the TMC Ocean Blue or Reef White, you would have more actual useful light energy (PUR) with these per watt of energy used (input energy) than the EcoTech (this is not to say the EcoTech Radion isn't reef capable LED).
More importantly, when you measure input wattage per output of mmol of PAR (which both are easily measurable), you can quickly discern that the Reef White is considerably more efficient. Please read the FULL article to understand why I made this statement.
Expanding a bit more, wattage input of lights versus PAR/PUR output is where the actual watts used when comparing one light to another is simply not at all accurate.
Keep in mind that PUR has nothing to do with input wattage. Moreover, PAR efficiency can vary due to PUR, fan use (fans waste input energy/watts), lenses, re-strike (in fluorescent lights in particular), and circuitry (such as daisy chaining of emitters common to many discount LEDs).
For example; the Fluval, Finnex, SB Reef, & Current Satellite are all Chinese made LEDs that often daisy chain their often plethora of emitters versus LEDs which use PWM, optimized PUR, and advanced circuitry/drivers with a lower number of HO quality emitters.
The result is a much higher wattage input per PAR output which the numbers speak for themselves as to the much lower light efficiency (sorry, math trumps marketing).
An example is the SB Reef Light PRO 32. This is rated at 363 watts input energy with a PAR of approximately 881 (100%) at 400mm of air. This comes to .41 watts of input energy per 1 PAR.
Another example would be the Fluval Fresh & Plant 2.0 A3990 which uses 32 watts of input energy with a PAR output about 70 mmol at 400mm. This is .45 watt of input energy per mm of PAR compared to an AquRay NP 2000 at only .08 watt of input energy per point of PAR.
To help indicate how colors will appear under different light sources, a system was devised some years ago that mathematically compares how a light source shifts the location of eight specified pastel colors on a version of the C.I.E. color space as compared to the same colors lighted by a reference source of the same Color Temperature. If there is no change in appearance, the source in question is given a CRI of 100 by definition. From 2000K to 5000K, the reference source is the Black Body Radiator and above 5000K, it is an agreed upon form of daylight.
A CRI of 100 has a heavy red spectrum. The color temperature is 2700 K for incandescent light and 3000 K for halogen light. An incandescent lamp, virtually by definition, has a Color Rendering Index (CRI) close to 100.
This does not mean that an incandescent lamp is a perfect color rendering light source. It is not. It is very weak in blue, as anyone who has tried to sort out navy blues, royal blues, & black under low levels of incandescent lighting.
Interestingly (& sadly), many lower end aquarium LED lights are matching their lights to CRI ratings. The results is a brighter light that looks good to us, often brings out colors to our human eyes, but are actually much less efficient for plant & especially coral growth. Two popular offenders are the Finnex & Fluval.
Common sense should tell one that the tropical noon time sun is 6500 kelvin and this it the optimum light for plant growth, not what looks best and brightest to us!!!
Reference: Specifying Light & Color
CRI is useful in specifying color if it is used within its limitations. Colors viewed under sources with line spectra such as mercury, GE Multi-Vapor® metal halide or Lucalox® high pressure sodium lamps, may actually look better than their CRI would indicate. However, some exotic fluorescent lamp colors may have very high CRI's, while substantially distorting some particular object color.
The picture below is a good example of marketing using CRI where by the picture on the right uses a halogen bulb source touted as having a "spectral match to daylight" and a CRI of 98.
HOWEVER the daylight picture to the left with the lower CRI is actually more accurate showing her hat as white instead of an off yellow which is typical of the lower kelvin lights also employed by lower end aquarium light manufacturers that tout high CRI.
To be blunt, CRI is NOT a parameter that is important in determining the best aquarium light, but it is included here since many mistakenly tend to consider it an important parameter, in fact most lights sold with CRI ratings prominently displayed are intended for home or industrial use, NOT aquariums! However many low end aquarium lights such as the Fluval LED Lights still refer to CRI since their PAR & in particular, PUR is poor.
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AQUARIUM BULB TYPE:
Aquarium Light Types Explained Here Include:
A standard pin, 1-1/2" wide bulb. The main caution to the use of these bulbs for aquariums, is the use of shop lights as an inexpensive alternative to many aquarium lights. A 4100 K cool white shop light is not going to come close to a 6400 K daylight lamp that is of peak PAR efficiency (even if you match lumens).
A standard pin, 1" wide bulb. As compared to the T-12, a 48" T-12 will use 40 watts, while a 48" T-8 will often use 32 watts (although not always), making the T-8 a more efficient lamp than the T-12.
Generally around 13 mm in diameter. This is a mini pin bulb which generally uses even less watts per lumen than many than T-8 bulbs. T-5 lamps range from 65 to 105 lumens per watt.
• One negative with T5s is that the quality control on these lighting fixtures (not the bulbs themselves) is often lacking. This problem tends to be with some of the HO T5 light ballasts/fixtures, and in fact tends to be a problem with VHO Compact Light Fixtures as well.
Another consideration for higher output requirements, especially hexagon planted freshwater aquariums, consider the SHO light over the T5.
Since I have seen a wide variance in quality of build as well as quality of output similar to with LED lights, I recommend going with the best and for this I would recommend the premium Giesemann T5 lights which have unique phosphor blends that are characterized by exceptionally high output performance, long life span, consistent coloration combined with high levels of spectral stability over time. In other words both quantity (PAR) and quality (PUR) of light.
The T2 lights measure only 7 mm and allow for several bulbs in a small space. A 13 watt 20 inch T-2 Bulb (6400 K) produces 950 lumens which is 73 lumens per watt in a very small space with low wasted green/yellow light energy that is often found in other Power Compact Lights!
These T2 lamps and fixtures are about the best fluorescent lamps in a small space I have seen! These are very useful for small to medium planted aquariums or Nano Reefs or even shelves for betta breeders (although ONLY as a compliment in larger aquariums over 20 inches in DEPTH for freshwater and 16 inches for marine).
The linkable fixture feature is also a nice aspect of these T2 lights/fixtures (this allows for use in larger aquaria such as 60 gallons).
Please Click the picture to enlarge
In fact these lamps are even a good choice for many aquariums such as 60 gallons and larger since each fixture can be linked together forming a larger fixture.
The Aquarium above is a planted 10 gallon with two 11 Watt T2 fixtures
One negative with the first generation T2 as compared to the older T5 is that there are not the selection/variety, however as noted in the previous paragraph, blue/actinic T2 lights are now available to the hobby.
Unfortunately, the plethora of cheap LEDs that have flooded the market (mostly from China) have pretty much killed the T2 light, despite the fact that often the T2 could out perform many of the lower end LEDs commonly sold when measured in input energy to output energy & results.
*VHO Power Compact
This stands for "Very High Output". These come in T-5 thru T-12 standard fluorescent tubes and in the newer power compact (usually 4 pin T6) lamps such as the Current USA, Coralife Quad & Via Aqua Helios VHO.
However both these before mentioned lighting systems are a bit pricey in my opinion for the "light output" for the price paid. As well the electronic ballasts contained in not just these, but ALL these VHO styles of CFL light fixtures (Current USA, JBJ, etc.) tend to have a short life span of under 3-5 years in my experience. When the ballasts go out, generally the replacement cost is the same as a new fixture.
I should also note that as of my latest update of this section (VHO), I have found their durability in relation to cost, and output in essential lighting parameters is not as good as T2, T5, SHO or especially LED Lights, which the LED in my tests, feedback, research and experience are the future of aquarium lighting, especially as it pertains to freshwater plant and reef aquariums.
*PC (or CFL);
This stands for "Power Compact" or "Compact Fluorescent Lamp (light)". These bulbs come in straight pin arrangements, square pin arrangements, and the self ballasted standard incandescent fixture "screw in" type. These bulbs are similar to T-5s and have about the same lumen per watt output (generally around 60-70 lumens per watt).
The standard medium base version of these lamps will fit in a common incandescent light fixture, making these lights about the most economical lights you can purchase with this kind of output. These are an excellent choice for use in low to medium light planted freshwater aquariums too.
See the picture to the left as an example, please click to enlarge
These self ballasted high PAR lamps are inexpensive and make it easy for even an aquarist on a budget (even a freshwater fish only tank) to provide the best possible lighting within a budget!
*SHO Power Compact Lights:
This "power compact on steroids" is another option for planted aquariums or hydroponics.
The SHO Light is currently sold in a self ballasted PC bulbs/light. The 105 Watt SHO Daylight bulb puts out 6300 lumens and is comparable to a 525 watt Standard bulb (click on the picture for a link). This comes out to 60 lumens per watt; however this is a deceptive guide, as you can fit many more of these bulbs in a given space and also utilize more efficient reflectors.
Product Resource: SHO & CFL Lights for Aquariums, Hydroponics
The SHO is already popular with Green Houses/hydroponics/cannabis growers and has a loyal repeat buyer following for planted aquariums.
My point is; if a company (greenhouse business) that needs the correct lighting that are price effective to grow plants for a business, all the more reason these should be considered in many freshwater plant aquarium applications.
The picture to the right displays a greenhouse start using ONLY SHO lamps (no sun).
In fact the medical community is now utilizing these SHO bulbs (& similar full spectrum lights, which is also often making the SHO in short supply) due to increasing studies that show better immune function, mental health, and more. Similar animal studies show like results. I learned of this when inquiring as to why the SHO lights were currently unavailable from the North American distributor, and they pointed out that several hospitals and convalescent homes had purchased over 1500 of these lights. They pointed out the simplicity of these Super High Output bulbs are quickly making these a favorite of the medical community for their full spectrum light needs (I now use a few 65 Watt 6400K SHOs in my home after learning this and there is certainly a difference).
There are few drawbacks to the SHO light for aquarium use; one such drawback is that in any "tube light" some of the light that shines up from each tube just reflects right back into the tube and is lost (this is called "Restrike"). HOWEVER, the spiral design & especially the use of an optional reflector tends to limit this minor problem and based on extreme plant growth achieved this is obviously not as much a factor as some may claim (this is essentially a problem with ALL compact Fluorescent lights).
Back to the positives of Super High Output lights; the cost per output of these lights is a major attribute of the SHO.
See also: Aquarium Plant Care, Information
Since the 6400K SHO requires as little as 2 to 2.5 watts per gallon for the most light demanding plants; Four 85 watt SHOs (or 105 watt for even higher output) can easily handle a 6 foot FW 125 gallon planted aquarium (some T2 or T5 can fill in some more dim spots if necessary).
The SHO can be mounted into your hood using a standard incandescent fixture. I recommend using an aluminum foil or better an easily made mylar reflector to amplify light downward (& reflect heat away from the canopy). I also recommend venting the hood to remove heat and moisture (a small outward direction fan can be helpful too)
The SHO light is most effective hung as a pendant light using reflector similar to how Metal Halides are commonly installed over an open aquarium. These SHO lamps are also an excellent compliment to MH, VHO or other "strip" lamps for use in reef tanks (in part due to their high intensity in small space and PAR output which is important for the symbiotic coral/algae relationship). Research (albeit older research now) has shown that many stony corals, clams, and other sessile species that depend on photosynthesis of zooanthellic algae not only thrive but also propagate when maintained under Power Compact lighting alone, and the SHO power compact has a MUCH higher useful light output over standard CFL.
The picture to the right shows one way of DIY mounting of a SHO light with a reflector by designing your own "rail" system that fits on the aquarium top. Multiple SHO Lights can be added with just such a mounting system
Please click the picture to enlarge
In summary as to SHO lights for aquarium use, what I find amusing is that the only negative comment I have had from someone who actually used an SHO in his 30 Hexagon is that his plants grew TOO FAST with constant pearling and he could not keep up with them due to his work schedule. Honestly this negative is positive proof of these lamps abilities!
*Metal Halide (MH);
Metal Halide was generally considered the "Kings" of reef aquarium lighting due to depth penetration, output, spectrum, and over all beauty and amount of coral life they help support making most corals "pop" with life (however the newest HO LEDs are now over taking the MH in many aspects of aquarium lighting).
That said for tanks over 30 inches in specimen placement, the Metal Halide is still generally the best available light, especially when used in light combinations that include 20,000K, with other popular Metal Halide Kelvin Color Temperatures being 10,000K, and 14,000K.
As for other light comparisons to the MH, even the newer T-5 lamps cannot achieve the depth penetration and overall output of these lights. Metal Halides generally have very good lumens per watt ratio (although I have seen a lot of variation and even incorrect ratings here); however it is safe to say that MH are generally found with lumens to watt ratios of 50 to as high as 90 which is among the highest of any aquarium lights available.
Metal Halide work via a gas mixture of halides and other elements, the actual light production comes from the small bubble of gas that is held in place by metal wires and/or supports. The electricity running between them and the small gas bubble, heats them, similar to an incandescent filament. This is one of the reasons that Metal Halide bulbs give off more heat than other bulbs.
MH Lights are generally sold in two basic types for aquarium use: the Mogul base & the HQI Double Ended Metal Halide bulbs.
The newer Halogen Quartz Iodide (HQI) lighting systems are used mostly on saltwater reef aquariums. HQI bulbs are commonly offered with spectrums of 10,000K and 20,000K. These high-intensity bulbs help corals thrive, but give off less heat than regular metal halide bulbs. HQI Double Ended Metal Halide bulbs have been used in Europe for many years have gained popularity in the U.S. among aquarium hobbyists in the last several years.
The downside is the heat that MH lights produce, often resulting in the need for hood fans and even chillers, although the newer open design units such as the EcoSystems USHIO double end fixture and HQI bulb works well for 10-25 or even larger aquariums when other lights are included in the "mix" without a chiller.
*LED (light-emitting diode):
Pictured above, Reef Aquarium including Acropora Coral at the National Oceanography Centre in London using AquaRay LED Lighting (Click to enlarge)
With higher efficiencies, these are becoming the new king of reef and planted aquarium lighting with many high end LED manufacturers such as AquaRay, EcoTech, Kessil, & Aqua Illuminations (among others) leading the way.
The better LED lights have the same shimmer effect and "popping" of coral life otherwise found in Metal Halide.
This aquarium light type uses semiconductor technology as its light source.
The difficulty in the past is correct wave length of the emitters, which in part are affected by the drivers/circuitry maintaining correct voltage over all emitters.
The high quality LED lights do not have as much of the heat problems of Metal Halide & even fluorescent lights (via ballasts), often last 50,000 hours, and some produce less of the yellow/green spectrum light which is less efficient for photosynthesis in many applications (in high-end aquarium LED adjusted configurations), and are very compact.
The new reef compatible & freshwater planted tank LED's are likely to take over the market along with the T2, T5, & SHO lights as the top manufacturers of LED fixtures become more readily available as the price comes down, while at the same time PAR & PUR (quality of light) & general aquarium compatibility come up.
Since LEDs emit light only in a very specific direction, the installer also has the option to illuminate a precise area using lenses in specific degrees of angle.
Common "Beam" angles include 120°, 90°, & 60° lenses. These can have a profound impact on PAR numbers too.
Achieving the correct wavelengths in the correct amount has been the challenge and why a simple LED flashlight has about as much in common to an advanced aquarium LED as a paper glider to an 747 jet airplane. This however is also the advantage as some of the less efficient light spectrums can be omitted with correct emitter bins and proper drivers/circuitry.
An example of a new emitter developed just for photosynthetically sensitive reef inhabitants is the 'Osram Olson NP Blue'. This patented emitter primarily targets the FULL spectrum of blue necessary for phototropic response, as well it also contains light energy in the full spectrum of PAR, unlike other blue emitters that have come before it.
In my opinion this is one of the most profound recent developments for aquarium reef LED lighting of late, as ALL other emitters used are either exact bins used for multiple generic applications or in the case of many licensed Cree emitters use emitter bins that are tweaked for aquarium use.
Another problem with many low end LED fixtures is even if the emitters used are of reasonably efficient bins, these LED fixtures "daisy-chain" their LED emitters together rather than provide the expensive drivers/circuity needed to maintain exacting voltage to each emitter. A plethora of LED fixtures are made in the same Chinese factories using the same lower "hardware store LED technology" under multiple brand names and sold at many aquarium stores and online big box sellers.
This driver/circuitry is partly important for maintaining spectral quality over all emitters without which the important PAR/PUR will not be optimal. As well voltage drops damage emitters which is another reason why many lower end LEDs have short warranty periods.
As well "pulse width modulation" (PWM) is best used for controlling the dimming of these emitters so there is no change to the spectral output as opposed to using "current reduction" (aka “linear or analog reduction”) used by many (most) brands of LED fixtures of which the result again is less than optimal PUR and wasted energy as heat instead of light energy.
As previously noted, this also results in more heat output and often the requirement of fans by these LEDs. This excess heat being driven away by fans simply equals input energy (joules) that is NOT GOING TO LIGHTING YOUR AQUARIUM!
Speaking of fans, besides the wasted energy, these fans make good water-proofing/resistance very difficult. This is why most LED fixtures have a water proof rating of IP66 or less. This means your electronic lighting device is being placed in a wet environment with a risk of failure over time or especially if dropped in the water.
Another aspect to consider is that unlike fluorescent, incandescent, and other lighting types; very specific emitters require circuitry/drivers similar to your computer.
Simply put, the more emitters along with more specific light output requirements, the more complex and expensive the circuitry and thus NO LED fixture is going to have specific output light energy with say 100+ emitters AND be even remotely close in price to one using 10 emitters if both are using correct LED driver circuitry.
It is also in the area of emitter development where-by development costs are incurred and where many who do not understand the business aspects of these costs, will then question why one LED manufacturer has or can have exclusive patent rights or similar.
What is also noteworthy is that these best licensed emitters can be driven at higher voltages. As an example, the standard XB-D White LED can produce 139 lumens when driven at 350 mA. However the licensed version (used in the GroBeam) can be driven at 700 mA producing 206 lumens with an efficiency of 86 lm/W and thus a much higher output than most LEDs used.
In the end, we can prove our LED Light's efficiency by comparing PAR at the same depth (15" of air is the standard). Using LED fixtures of similar lens angles (120/unlensed to 120, 90 to 90, etc.).
Reference: Cree XLamp XB-D
Controlled Tests with Plants and The Aquatic Life Implications;
As previously noted in the "Useful Energy Section", tests for plant nurseries (Green House, Hydroponics) full spectrum LEDs such as the newer generation AAP GroBeam Aquarium Lights, LED Grow Lights, or even the older generation LED Grow Lights have been proven to surpass even Metal Halide Lights in both growth and useful output.
The picture to the left is the plant growth results comparing the same Kelvin output LED and Metal Halide Lights as measured by a PAR Meter (please click to enlarge view).
Implications of these tests:
Reference: PUR in Aquarium Lighting; Depth Penetration
It is still easy to make assumptions from the raw data based on this study with plants that a 12 Watt High Output LED should easily replace one 175 Watt Metal Halide MH of similar rating for marine applications.
Product Resource 12 Watt examples include:
Below is 5 foot 100 gallon reef aquarium with only four AquaRay 600s (2 Marine blue & 2 Reef White 600s).
However, of late, this history has been lost due to slick marketing of over the top energy wasting LED fixtures that actually do little to improve plant or coral growth, but like light fixtures of old produce copious amounts of heat that creates further issues, including shortening the life of fixtures employing such methods.
This is not to argue that there is a place for entry level LED lights, just do your home work and understand that purchasing high input wattage lights does NOT mean you are getting the most efficient LED.
Product Sources to support this FREE information:
*Aqua Illuminations Hydra Twenty Six HD
VIDEOS:Video for an aquarium with three AAP Reef White LEDs & two CFL lamps:
Video with a AAP 1500 NP Ultima Ocean Blue (over a 29 gallon aquarium)
Video with reef aquarium utilizing AAP Ultima NPs, Reef White 600 Ultimas, and PAR 38 LEDs:
More about Emitters:
As I noted earlier, not all emitters are equal even with the open source Cree emitters, commonly sold for other applications. These are only as good as their correct wavelength output (Kelvin Temperature/Nanometers). One cannot compare a computer that uses an exclusive patented Intel processor to one that uses maybe a similar, but generic version of this processor. As with a computer processor company, an LED emitter manufacturer is going to have exclusive licenses/patents as well as generic versions.
What's noteworthy is the latest licensed version of even the newest Cree emitters are not available over the counter to even to the majority of LED builders that do NOT have the license rights.
Far worse yet would be the cheaper no name emitters used by manufacturers such as BaiSheng, Epistar, & others sold under a plethora of other names for so-called aquarium use. These use daylight emitters that can vary widely in Kelvin Color output from only 2000K to 6500K and are in reality generally much less efficient for photosynthetic aquarium life use other than just plain light!
Based on email I get, forums I regularly read, & YouTube videos (for DIY LED Aquarium Lights), many seem to make this very INCORRECT assumption about emitters, drivers, PWM, wasted heat energy, etc.
These same older generation emitters, controller technology & drivers are the reason I did not recommend LEDs of ANY brand for "higher-end" aquarium applications until 2008 (readers of this VERY constantly evolving article in 2007 would note this too).
As noted earlier, another common LED emitter usage is "cool white", "warm white", and "neutral white" by many LED manufacturers so as to obtain necessary efficient PAR spectrums and a pleasing color through a shotgun approach. These same LED manufacturers then disguise their LEDs using "cool features" and ramped up input wattage to drive high PAR numbers to sell these otherwise inferior LEDs as per PAR/PUR delivered for wattage used.
Often these colored emitters are used to allow the user to blend colors so that many of these LEDs can be used in both Reef and high light planted aquariums.
I should also remind readers that when tuning in specific color combinations, this results in 40% or more loss of stated PAR output since not all emitters are running at full potential. HOWEVER, this is not the case of the Aqua-Illuminations Hydra HD since this LED allows the user to drive light colors at more than 100% when another color is turned down (so that 100% of the input energy is indeed utilized).
This said, this does not make these LED fixtures bad, just less efficient using much more input electricity for the same results and often this results is lower PUR spectral efficiency and fixture lifespan (hence the one year warranty of most of these high end lights that perform all these functions).
Another noteworthy FACT (as noted earlier in this article) is the green light energy produced by these fixtures is less useful for Zooxanthellae photosynthesis and these same photosynthetic marine life have adapted to an environment of much more blue nanometer bands of light energy and little red is required nor does it penetrate!
For the lower quality build units using multiple daisy chained emitters (often dozens) and poor drivers, the end result is many of these albeit reef capable LED fixtures such as the Taotronics require 120 watts of input electricity to produce the SAME PUR as a 30 Watt AquaRay AquaBeam Ultima due lower emitter PAR efficiency, the use of "Current Reduction", and along with other circuitry design issues expend more heat energy that could be going to light energy.
In electricity alone at the average USA cost of .13 per kWh, run at 12 hours per day this 90 watt difference equals a $51 savings in just ONE year!!
Then throw in a shorter warranty (as low as 180 days) and a water resistance rating that does not fully protect your electronic light emitting device and what have you got in price savings when it goes belly up in a year or two?
Another misunderstanding about LED emitters is targeting the responsive wavelength. While exact coral responsiveness wavelengths are unknown, much is known in a more broad sense (and even more knowledge is growing, such as the "blue band" of coral responsiveness). For example, we do know that much of the yellow and green bands are 30%-80% less efficient for most photosynthetic corals, clams, etc. (although under 24% green light can be useful, but over 25% it is actually detrimental; Reference: Ref. 1)
This has been a controversial topic in a few fragging circles, when it comes to a few red corals such as Red Acans. I have found little to support the claims that these corals fade to orange under correctly applied LED Lights.
Since many over load on blue emitters, and admittedly most "better" LEDs lack as much of the yellow nanometer light cyanobacteria need to thrive, I feel this (along with specimen placement) is the possible cause and why those who use a good mix of LEDs or even LEDs with T2s or T5s have not observed this phenomenon.
Use of LED to prevent Red Slime
The bottom line is when you compare an LED Aquarium light to the many popular CFLs and even T5s in terms of lumens per watt, focused lumens, PAR, PUR, lower wasted yellow/green light energy, low heat output, energy consumption, long life (25,000 to 50,000 hours vs. 8000 hours), the modern recent generations of LED Fixtures are generally the best available aquarium light.
When compared to even older T8/T12 aquarium lights, a forth generation AAP AquaBeam & GroBeam High End LEDs require only 15% (or less) of the wattage for the required light energy of a planted or reef aquarium.
Any flaws of LED aquarium lights are quickly disappearing and based on the energy savings for the premium high PUR LEDs with PWM technology as compared to MH.
Retrofit is also not all that difficult with most better LED systems sold with hardware that makes DIY mounting options quite varied.
LED Light systems are easily complimented with T5 Fixtures, T2 fixture for smaller applications, or even the SHO self ballasted high output CFL for large tank applications.
Finally;, I should note to newer readers of this constantly evolving article that may think there is bias toward high end LED lights, you would only be 1/4 correct, as first I do not recommend the plethora of junk LEDs commonly sold and as well if you were to read this same article circa 2007, I did not recommend ANY LED Light, however technology had increased considerably in this arena of aquarium lighting.
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Often LED as noted above are used as lunar or moonlights. This is an area where anecdotal information seems to be the main information available.
This includes the common belief that moonlight should be "blue" when in truth all the moon does is reflect diffused sunlight back to the earth (more during full moons, less during other phases). Dust or moisture can affect the color spectrum seen by the human eye as well (which often makes the light appear blue). This means that a dimmed/diffused daylight is a more accurate production of moonlight. This can be done by fading a Reef White AquaBeam LED as an example.
Essentially these are very popular for marine reef aquariums for both a low level "night light" and for simulating moonlight for corals and coral propagation.
Where some of the misinformation comes into play is that many will state that fish need these lights, of which there absolutely no scientific proof and also that corals need these for proper growth which also has no scientific evidence to back this up.
What lunar lights (moonlights) could do with correct programming for the marine reef aquarium is to simulate marine lunar cycles which are necessary for some fish and coral reproduction/propagation, as Corals in the Great Barrier reef spawn 3-7 days following the first 2 Full moons in late spring and early summer. Even here there is still a lot of controversy as to what cycle is best and how much light is best.
From what I personally have observed combined with the opinions of other aquarium professionals is the use of gray nylon filter placed over standard daylights (T2, T5, T8 CFL, etc.) can work as a moonlight; even low level "white" lights such as nightlight bulbs, or even the Rio Mini Sun LED lights can work just fine for this since this has shown to be a more of a low level light issue and timing issue.
Adding or subtracting the amount/intensity seems to be the secret of simulating these cycles which can be accomplish easily either manually or with electronic timers (that can be set to more accurate monthly 29.5 day lunar cycles of lighting). Strategically placing these lights also shows evidence as to properly simulating this effect.
Please click on the picture above/left for a larger animated version of the lunar cycle
HID stands for "High Intensity Discharge", this technology is currently used in high end luxury cars, however there may be aquatic implications here in the future as PAR and other potential issues are worked out. HID lights use an electrical charge to ignite xenon gas (a colorless, heavy, odorless noble gas, which occurs in the Earth's atmosphere in trace amounts) contained in a sealed bulb. The technology of HID automotive lamps is similar to that of common vapor-filled mercury vapor street lamps.
These Xenon HID lights seem to produce much in the lower chlorophyll A segment of PAR, but currently not as much in the higher infrared part of PAR.
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Important Parameters to consider when choosing a light for your aquarium (not a complete list):
The watts per gallon is part of the lighting equation as stated above is highly inaccurate when taken by itself, yet may in the aquarium hobby industry still go by this outdated generalization which leaves me scratching my head with all the advances in lighting technology. Taken together, the first FIVE points are the most critical (which does include watts per gallon), but no one of these should be a sole determiner of the lights.
Even a "105 watt Super High Output (SHO) Light" which is an excellent light, especially for planted freshwater or hydroponics applications, when compared apples to apples to the 30 watt GroBeam 1500 Ultima only produces 85% of the same useful light energy despite using more than triple the energy.
This is not to say the 105 SHO is not a good light, far from it, especially when one considers the vastly lower price and that this SHO light still out produces most any T12, T8 and T5 (using 6500K for all comparisons); as a generalization (assuming equal Kelvin) the SHO requires only 2 to 2.5 watts per gallon for a "high light planted aquarium".
Lighting Time & Replacement
Here is a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening.
ANY fluorescent light used for aquarium applications such as planted aquariums or reef, slowly burns up phosphors and other rare earth elements that produce the light energy necessary for PUR.
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