  AQUARIUM LIGHTING INFORMATION GUIDE | Reef Planted | PAR PUR/PASComplete Facts & Information To Help In Understanding Kelvin, Nanometers, PAR.
Written with professional experience & research since 1979. |
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(1) Aquarium Lighting Factors (2) Kelvin Rating (3) Nanometer Range (Spectrum) (4) Lux (5) PAR (Photosynthetically Active Radiation) (6) Measuring PAR (7) Quality of Light (PUR, RQE, PAS) (8) Photoinhibition (9) Lumens (10) Watts (11) CRI |
(12) Aquarium Light Type |
(13) PWM (14) Parameters (15) Light on time & change (16) Lamp placement (17) Light Penetration (18) Specimen Placement (19) BASIC LIGHTING SET UP SUGGESTIONS (20) Summary (21) PDF of this Article (22) References |
AQUARIUM LIGHTING, Information including Factors, Types, & Use
By Carl Strohmeyer- PAMR 40+ years experience
Updated 3/31/20
Video version of the first section of this article:
Aquarium Lighting 2018 | Kelvin, PAR, Watts and More
Recommended Companion Article:
PAR in Aquarium Lighting
OVERVIEW
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 Often this would range from 3 to as much as 5 watts per gallon, but this now is quite outdated for most modern lights.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.
SOME HISTORY/COMMENTARY:
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;1: KELVIN RATING (such as 10,000K daylight bulb):
What is meant by Kelvin Temperature of Lights is not the classic interpretation of the meaning of Kelvin.
Light Kelvins
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.See the picture example below:
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:
- While our coral & plants are not black body radiators, THIS IS IRRELEVANT since Kelvin in our usage is simply a predictor of light spectrums
- Plant chlorophyll absorbs light at wavelengths of 300 to 700 nm Kelvin rating of about 6400 strikes a good balance here, which is why this is the best Kelvin temperature for freshwater plants (& symbiotic zooxanthellae in corals in shallow, perfect conditions).
- The lower the "K", the more yellow, then red the light appears, such as a 4500 K bulb.
- The higher the "K", the bluer the light appears, such as a 20,000 K bulb.
- Higher Kelvin Color Temperature lights penetrate water more deeply, even more so in saltwater, however there is less of the red "PAR spikes" as well.
- The human eye mostly sees light around 5500K.
- Candle flame = 1850 – 1900 K
- Sunlight (1 hour after dawn) = 3500 K
- Typical summer light (sun + sky) = 6500 K
- Cool white fluorescent = 4200-5500 K
- Different nanometer wavelengths can be used to reach the same Kelvin Temperature; just as 4+5 & 1+8 both equal 9, so can different nanometer wavelengths be used for the same Kelvin Temperature.
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 Warm White (2700-3500K) & Cool White (4200-5500K) are typical lighting kelvin ratings used in home lighting and is common of lights sold in hardware stores, etc.
While these sources were used years back for both planted and even reef lighting out of necessity (as there were not many options available), these are poor choices due to little essential PUR energy & many more cool white and especially warm white lights are required to delivery this light energy for photosynthetic life.
While these may work and even look pleasing, IF YOU ARE LOOKING FOR THE HIGHEST OUTPUT IN USEFUL ENERGY PER WATT OF ENERGY CONSUMED, these kelvin color lights/emitters should be avoided! - The 6500-8500 Kevin lamps have produced the best terrestrial plant growth and generally the better freshwater plant growth (as this Kelvin lamp generally has more of the 'red' nm spikes needed by "higher" plants, but still has some of the 425-500 nm blue).
More importantly if a natural tropical noon time sun 6500 light is utilized, you will get a better balance of all colors over a mixing of colored LED emitters so popular with planted aquarium keepers who like this red light over their red plants who also think this is better for the plants, which simply is not correct based on many years experience utilizing many different light sources. It is the balance that you should seek.
See the section about Light Time/Placement where I demonstrate that as fluorescent lights age, they produce more red & yellow, yet plant plant growth decreases (& yes this applies to ANY imbalance of red & yellow light, not just from fluorescent lights).
Please note that saltwater absorbs slightly more light energy than freshwater due to the higher density of the water, so 6500K lights will not penetrate as deeply and are not a good choice for depths over 12 inches. - The 9000-10,000 Kelvin lamps also achieve good growth rates, although slower than the 6500 K bulbs in shallow aquariums. 9000 to 10000K bulbs have produced excellent growth with soft corals & LPS, although slower paced SPS growth.
The 10,000K can be a good choice for achieving PAR for better depth penetration than a 6500K bulb (such as 12-20 inch or even deeper aquarium). - The 14,000K light/lamp, will penetrate even more than the 10,000K light while still providing useful PAR (this would be the highest "Daylight" Kelvin temperature I would recommend and still expect good growth in corals. An excellent daylight color for tanks between 15 & 30 inches in depth.
- The 20,000 K light/lamp is more blue yet, and brings out all of the fluorescent pigments in many corals making for a very nice appearance. However the many tests and observations show that when used alone, except in tanks over 24 inches, the growth rate of SPS corals can be slowed or even come to a standstill with 20,000 K lamps.
See Reference:
PUR vs PAR in Aquarium Lighting
Kelvin Summary
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.
2: THE NANOMETER RANGE (SPECTRUM)
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.
3: LUX:
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.
4: PAR:
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, c², 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 c².
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.
Important Definitions as it applies PAR in plants & zooanthellic algae:
*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.
- Besides the obvious depth penetration, it is also noteworthy that most zooanthellic algae need more of the blue spike than "higher plants", hence the popularity of actinic lights for reef aquariums. However the general optimum nanometer range is about 450-485nm.
For this reason it is a good idea to have extra actinic for corals/clams that depend upon zooanthellic algae, while at the same time limiting blue/actinic in freshwater aquariums to avoid excessive green algae growth. An advantage of the latest technology LED lights is having a more precise 450-485nm blue as well as some 420-450 nm Fiji/violet lights/emitters for certain deeper reef specimens.
As well, a popular trend in LED lighting is to utilize NUV light /emitters that emit light energy between 300-400 nm, HOWEVER as per current known science this light energy is is mostly useless for your photosynthetic life and is generally WASTED LIGHT ENERGY! Part of the reason for this trend is that this makes many corals pop with color since this light range is similar to a black light, but if used, this light energy SHOULD NOT be counted as part of your necessary light energy.
As an example, if your Light is 140 watts but has 20 watts as NUV blue, you essentially have a 120 watt light! - Planted Freshwater Aquariums: It is also important to note that freshwater algae also prefer more of the "blue" light so the excessive use of actinic blue lighting should be avoided in planted freshwater aquariums, as well the use of more blue nanometer or higher Kelvin Daylight (14,000K or especially 20,000K) should also be avoided in all but the deepest tanks or in tanks with heavy amounts of C02. Otherwise many freshwater plants may not be able to "out compete" against some algae such as hair algae.
- More recent studies show that UVB radiation can bleach coral, so the use of blue lighting under 320nm should be avoided!
Measuring PAR
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•m²•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
*Further reference:
*Photosynthetically Active Radiation
*Fish Health:
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.
Further Reading:
Aquarium Disease Prevention
5: RQE, PAS, & PUR, "Quality of Light"/ "Useful Light Energy":
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/left 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 also noteworthy that as we gain knowledge, we can in fact map the optimal PUR for a given species such as pictured/graphed below for the stony coral "Favia" which is a species that is more adapted at deriving energy from the middle spectrums, albeit still less efficiently
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.
The picture to the right demonstrates how three LED emitters of equal lumen & PAR output can be quite different in PUR and thus more of the less efficient yellow/green energy.
The other term that is thrown around is "Quantum efficiency"; this term generally refers to the efficiency to incident photon to converted electron (IPCE) ratio of a photosensitive device which predicts a 30% lower efficiency in green spectrum (see diagram in PAR section).
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
Reference also cited for this explanation: www.ncbi.nlm.nih.gov
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".
- I have noted, a dozen "hardware store" warm & cool white fluorescent lights can provide adequate lighting for a planted aquarium and even basic reefs. However, it would only take a few optimum kelvin T5 lights to accomplish this same task.
The point is, even a T12 cool or warm white provides some useful light energy, but it requires a higher number of these lights (& input energy) to provide adequate light in both quantity and quality for our application of plant or reef aquariums. - One could use nothing but mid range PAR green emitters, versus using an emitter such as the Osram Oslon NP Blue with the same input wattage and actually obtain a higher PAR, YET the Green emitters are as much as 80% less efficient than blue emitters as references cited previously prove!!
For further reading about PUR:
*PUR vs PAR in Aquarium Lighting: Why PUR is Important
Below is a picture of a Reef Aquarium (88x32x24”) that includes Acropora corals lighted with ONLY VERY high PUR but lower wattage AAP AquaRay NP 1500 & 2000 LED lights (this tank has been running with these lights for 6 months at the time of the picture).
6: PHOTOINHIBITION:
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·m²·sec. At 350 µmol·m²·sec the rate of photosynthesis was about that seen at 75 µmol·m²·sec!
Further Reference/Reading:
The Myth of Corals Requiring Unlimited Amounts of Light
7: LUMENS:
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.
Focused Lumens;
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.
8: WATTS:
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.
9: CRI:
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.
AAP AquaRay; Ultra Premium LED Aquarium Lights, Planted, Reef, more
AAP Reactor/FSB Filters
TMC Advanced RO Filter System with TDS Meter
More efficient than popular discount models.
