an example of the inaccuracy of the watts per gallon so-called rule, please consider these comparisons for an assumed 25 gallon aquarium:
* 20 watt T12 light with a Kelvin temperature of 5000 K,
Compared to a:
*20 Watt
LED with an adjusted Kelvin temperature of 6500 K.
So assuming you would like 4 watts per gallon (this “rule” came about when T12 & T8 were the most common lights), you would need
five of the described 20 watt T12 lights.
HOWEVER, once the other important factors are applied the described LED is shown to require vastly less wattage to produce similar results than the T8/T12 bulbs.
*PAR; the LED is more than 25% higher, as well many current LED emitters designed for aquarium and plants are more than 50% higher.
As well the useful light energy adds at least another 25% for an increase of 50% in this area of light output
*Focused Lumens; the LED 166% more efficient in focused lumens (about a 2/3 reduction of necessary watts)
*Lumens per Watt; the LED is double the lumens per watt.
In a rough math equation using a starting point of 100% of the T8/T12;
100 less 75%= 25% less 67% (2/3) = 8.25% less 50%= 4%
In other words you would need 4% of the wattage to provide the same lighting as similar watt fluorescent aquarium light
This would roughly result in
just one (actually less, and you will still have more light) of these lights for the same tank size (a 25 gallon in this example).
As you can see the watts per gallon rule falls apart in this comparison, in fact in this comparison one watt of high output emitter LED has a higher output of usable light than the 25 watts of the T12 (100 divided by 4). Of coarse the differences can vary, so even this comparison only works for the described lights and tank, this is also based on the newer Cree XR-E Power LED emitters employed by TMC (and some PAR 38 LEDs) which have a high output of useful energy.
In fact based on raw data from controlled tests, even the modern comparable Kelvin HO T5 lights or Metal Halide which are so popular do not hold up in comparison to a modern LED with the Third Generation AquaRay LED emitters. This data indicates that a modern LED requires 14-28% of wattage for the same useful light energy output.
Even then a T5 or even more so a
T2 are vastly superior to the older style aquarium lights when all criteria are applied (SHO as well are also superior).
