AAP UV Sterilizer ExpertsUV Sterilizer Dwell Time

UV Sterilizer Dwell Time Experiment, Effect on UV-C Sterilization

Test Between Compact UV and Straight Tube UV

Comparison of UVC Dwell Time Between T5 & T8 UV Bulb

UV Sterilization and Dwell Time Comparison PDF

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Updated 3/5/21


UV Sterilizer Dwell Time

A Controlled Experiment
between a Terminator 13 Watt UV Sterilizer (which is one of the best compact UV Sterilizer designs as per water contact design) VERSUS a TMC Vecton 8 Watt "High Dwell Time" UV tells the story of UVC Dwell Time:

Using a Rio 600 (200 gph), with 2 feet of 5/8" ID tubing; the dwell time inside the Vecton was 2.6 seconds, while the Terminator was 3 seconds.
It is important to note that the Terminator holds DOUBLE the water volume at 20 oz. water (meaning a less efficient design with more water not within the optimal 3 cm exposure zone) versus 10 oz. of water for the 8 Watt Vecton. Keep in mind that the Terminator is one of the best designed Compact UVs, as it is noteworthy that the Turbo Twist has an even higher water volume due to even less efficient water contact design.
The result is 6.66 ounces of water per second is exposed to UVC irradiation for the 13 Watt Terminator while 3.84 ounces of water per second is exposed to UVC irradiation for the 8 Watt Vecton. MORE IMPORTANTLY the results are 1.95 watts of UVC energy per second for the Terminator 13 watt versus 2.08 watts of UVC energy per second for the 8 Watt Vecton.

What does this mean? The Terminator is a very good compact UV (among the best from our maintenance companies experiences, comparing favorably to the Tetra and better than the Jebo, Aqua Top, Coralife Turbo Twist and others), HOWEVER when you consider the 8 watt Vecton actually has a higher dwell time due to actual time per ounce of water held close to the UVC lamp and although the 13 Watt Terminator has a higher energy output, the lower dwell time basically renders these two UVs equal in aquarium/pond gph capacity.
So with the TMC Vecton (the same goes for the TMC Advantage), you will be getting more UVC Sterilization per watt (as well as a more durable long life UV compared to ANY Compact UV Sterilizer or Clarifier. This higher level with the same or often even lower input wattage can also be shown with higher simple heat transfer too (in other words the normal heating observed with UV use will be noteworthy with higher dwell time for the same given input wattage).

Better yet in the case of the super high efficiency Pro Clear UV55, this same test yielded 2.29 watts of UVC Energy per second with an "apples to apples" adjusted flow rate of 750 gph (8.17 watt per second with the same Rio 200 pump).

Product Resource: TMC Pro Clear UV55: High Efficiency Pond/Aquarium UV Sterilizer

The bottom line is a Premium High Dwell Time UV with almost 100% water exposure to UVC irradiation under 3 cm that is of less wattage is going to out perform a well designed Compact UV of higher wattage (many compact UVs are not of the design either of the Terminator)!

Comparison of UVC Dwell Time Between T5 & T8 UV Bulb:

In the previous test, the Vecton 8 Watt utilizes a T5 UV Bulb, but what about the common T8 UV Bulbs used in many larger UV Sterilizers versus a T5 of similar size?
This is a good question, yet also has some misunderstandings too (that I too have made).

While T5 lamps are roughly 16% more efficient at converting electrical energy into light energy, this does not necessarily make the T5 the better lamp as some have stated.
Given two lamps of equal length, equal UVC light output, and equal flow rates, then the dwell time will be the same, and the germicidal effectiveness will be practically indistinguishable, regardless of the number of electrical watts pumped into each one.
As an analogy it is like saying that if my car goes 140 mph with a 200 hp engine, and 160 mph with a 300 hp engine, then a 300 hp HYBRID engine (using 16% less gas) will make my car go 180 mph (as per the logic of using a T5 over a T8 UV lamp).

Also, if the manufacturer uses a 5/8" diameter T5 instead of a 1" diameter T8, and reduces the tube sleeve diameter by 3/8" (compared to a T8 fixture), and then reduces the reaction chamber diameter by 3/8" (to stay within 3cm of the tube sleeve); in that case, the T5 fixture will have a smaller cross section area, which will REDUCE the dwell time for any given volume flow rate.

Reference: Everything Aquatic Forum: UV Sterilization

As an example, a 57 watt T5 as used in the Aqua 114 watt UV is 17.5 inches long (two lamps are used), while the 55 watt T8 UV bulb used in the TMC 110 is 36 inches long (two lamps are used).
Next we factor in the higher energy input (57 versus 55 watts), we would presumably have 4% more raw output of UVC energy.
But next we have to figure an exposure time that is spread over twice the length of bulb and this is 100% more dwell time.
So 100 minus 4 and we get 96% more effective for the TMC 110 over the Aqua 114 UV!!!
It is also noteworthy that "Emperor UV" also uses primarily lower dwell time T5 UV lamps.

Product Resource: TMC 110 Watt Professional Large Pond/Aquarium UV Sterilizer

Aqua UV versus TMC UV Sterilizer
Aqua Pond UV vs TMC AAP Pond UV Clarifier Sterilizer

This might not be the case in every T5 to T8 comparison, but in many comparisons the slightly lower efficiency is trumped by the longer dwell time, so we cannot necessarily make the case for T5 being the better UV bulb.
In fact watt per watt, the 36" 55 watt Pond Pro Clear UV has no equal as most comparable wattage T5s are only 19-20" in length.


Please click on the "Buy Now" Button below for a pdf format downloadable e-book (41 pages) of this article as of 7/11/14 for $3.99 usd. This includes Both the Full UV Sterilization and the Dwell Time Comparison Article.
This can be saved to your iBooks, computer, printed for easy reading Computer, etc.
Please understand this fee covers the time to format and our fees to Adobe to generate this PDF article.

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