My hypothesis with lighting by watts/g

[liberator123]

I tried to figure out a way to "compare" the different lights based on apples for apples kind of thing (t8, t5ho, LED). I have no idea if I did this right or not, if it was a total miss, but just hear me out. I did a lot of reading to do this lol...
-60 watts of incandescent light is compared with 15 watts of fluorescent, so I will use 15 watts as a constant value for my calculations. (7-8 watts for LED)
-We used to follow the rule for t8/clf fluorescent 1watt/gallon low light, 2watt/gallon mod light, 3watt/gallon high light
-Thus, a 10 gallon tank will need 30 watts for high light... so 2X 15watt fluorescent bulbs
-t8 is almost equal to cfl in terms of watts
-From source:
"Type of Bulb Lm/W
Incandescent 5-18
Halogen 20-25
(CFL) lighting 45-75
Fluorescent 45-125 (t12-t5HO)
LED 10-150"
-From source1 source2
4 t5ho approximately equal to 6 t8ho in terms of total lumens. (though not exact, there is a 2000 lumen difference)
-In their example, t5ho would be about 1/3rd more or %50 more effective. This almost makes sense if we take the highest lumen/watt cfl rating (75) and the highest t5ho rating (125). (about %60 more effective)
-Commonly, a 15 watt 6500k t8 tube is about 60 lumens/watt (based on many comparisons in google). However, there were many different t5ho lm/w values, and there isnt such thing as a low watt t5ho like 15w, but mostly were around a 40-60% more efficiency (8X-9X lumen/watt). Therefore, these are not exact values, just estimates (like almost ALL electric related values... *american homes give out 110-120 volts, not a set number anyway*)
-So I assume that many t5ho is about %50 more effective than t8. Thus a 15watt t8 should equal to a 10watt t5ho
-Thus: 2x 15watt t8 = 2x 10watt t5ho = high light 10 gallon tank
-Therefore, the watt/gallon rule for t5ho is 2 watts/gallon high light, ~1.3watts/gallon mid light, ~0.7watts/gallon low light.
-Now lets try to apply this to LED: Source: 15watts CFL = 8watts LED.
-Depending on the Lumen count of the LED you are getting, you can calculate approximately how much Watts/gallon you will need for low/mod/high light. Note that LED is kind of wierd to calculate because there are many different sizes... and 10-150 lumens/watts is such a big range... Not to mention, it is digitally based technology.
-example: an 8 watt LED 6500k (most of the bulbs I look at are at this kelvin) bulb I found online is 640 *here*, another I found 7 watt LED Tube (size of a t8) that was 7 watts for 700 lumen *here*, even another, 8 watts for 760 lumen *here*. I will take 7 watts for 700 lumen, so that is 100lumen/watt.
So, if LED 100Lm/w = Fluorescent 60Lm/w, then LED is 67% more efficient in terms of wattage.
Another calculation is as follows: 8watts LED = 15watts Fluorescent, thus 16watts LED = 30watts Fluorescent (which is high lighting for 10 gallons following 3watts/gallon rule). So if 30watts/10gallon divided by 10 is 3watts/g, then 16watts/10gallon divided by 10 is 1.6watts/gallon. 1.6/3= 0.53 x 2= 1.06. Therefore, LED "should" be 0.53 watts/g for low light, 1.06watts/g for moderate light, and 1.6 watts/g for high light.
Now, one must factor in the effectiveness of each watt (lumens/watt) in comparison to the Fluorescent bulbs (which is what we are using as a constant). Since the particular LED tube had a 67% more effectiveness for each watt, that means the watt value of the total watts should be 67% more. That 8 watt LED true watt value would be 13.36 watts. That would mean: that single 8 watt LED tube "should" give middle between moderate and high light for a 10gallon tank. (1.06-1.6watts/gallon : 10.6 -16 watts/10gallon)

So, for one to "calculate" the watt/gallon rule for a non cfl/t8 tube, one should also factor in the effectiveness of the t5ho/LED, which are not all the same so it seems. The way I did it was to compare the Lumens/watts. Of course the limitations of my research was that I do not have any experience with any of the t5ho/LED tubes for aquariums (im actually still a newbie in the hobby). In addition, I do not have any means to test my hypothesis as I do not have a PAR machine to see if my theory is correct. What I found in the rough estimates of my calculations are:
Type, Low watts/g, Mod watts/g, High watts/g
t8/cfl, 1, 2, 3
*t5ho, 0.7, 1.3, 2*
*LED, 0.53, 1.06, 1.6*

*(however one must calculate the effectiveness of Lumens/watt in compared to t8/cfl to get the "true" watt value of the bulb/fixture you have)*

I would like to apologize if my hypothesis is completely wrong since I never factored in PAR (I wanted a way to see if watts/gallon rule can still fit in the newer technology). At least I tried... tell me what you guys think!

 

[Mebbid]

I see what you're trying to do there and it was obviously a lot of work. The biggest issue I have isn't about the bulb calculations but is instead the light fixture itself.

For example: A t5ho can have drastically different par levels based on the reflectors that it has on it. The same 2 bulbs in one fixture could be high light with highly polished individual reflectors but in a different lower quality fixture it will give you a solid medium light level.

This picture shows a general difference in par between different fixtures with different reflectors.

LED light is even more difficult to average out to different light levels / wattage. This is partially based off of the lenses that are on the lights as well as their construction. Some manufacturers will make a fixture using 3w bulbs and force the fixture to run at maximum 2w to extend the bulb life. Adding in lenses to that which narrow the focus of the beam dramatically from a 120 degree area all the way down to a possible 40 degree angle means there is a HUGE range of possible light levels for a single given bulb.

Furthermore, lumens are a highly inaccurate way of determining the par levels of a light which is by far the more important measurement.

 

[liberator123]

i see. yeah i figured that there were too many factors involved to just look at one calculation. but it was worth a shot. hehe. but i wonder if i can set the reflector and distance from tank as a constant value that was used to determine the w/g rule for t8 and THEN compare it to the others.

 

[aqua_chem]

Your math is well founded (I have a special place in my heart for dimensional analysis), but you have only considered bulb efficiency. You also have to consider ballast quality, heat exchange efficiency (or active cooling, god forbid), reflector quality (which mebbid brought up but deserves repeating), and more. It's simply an unworkable rule that needs retiring. I hold it in equal esteem to the adage 'whoever smelt it, delt it'.