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I'm confused about LED lighting...I looked at 36" Finnex 24/7 that states it uses 72 (wattage unspecified) LEDs for 16.9 watts (lumens unspecified)...Beamworks 36" uses 24 3 watt LEDs for 72 watt, 3240 lumens.

I have a dirted 40 breeder with pressurized CO2 [36(L) x 18(W) x 17(H)] and want high light to grow foreground carpet. Is the Beamworks 4 times brighter?
It seems to me I've seen a lot of tanks with 2 strips on the top. I'd rather have to buy only 1 light!

How does one figure out how many watts/lumens/LEDs to use?
 

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First, most LED "strip" type lights don't cover a 40 front to back and top to bottom..
Second wattage is a hard metric to judge LED lights buy. It is prone to a bunch of "errors" from low watt efficiency to the difference between LED watts and system watts.
finding some PAR readings will help here.
There are posted ones for both of these.. sort of..Beamswork needs a bit of interpretation.But it can push 65PAR to 17" approx..
24/7 is 48PAR at 18" on FULL, which w/ the 24/7 is really only a short-ish period of time.
no, the Beamswork is not 4x brighter.
most of the discrepancy comes in the fact that lumen efficiency of the different diodes is different. Like 50L/w for a Beamswork and probably close to 100L/w for the Finnex..
The advantage of a Beamswork over a Finnex 24/7 only lies in 1)REmoving lenses will spread the light better on a 40. 2)raising, as opposed to removing lenses) will lower PAR less (more to begin with) than raising a 24/7
If all that matters is the front portion of the tank, well then it doesn't matter.
Third, due to the rise/fall lighting of the 24/7 in 24/7 mode its output varies considerably by time and if you just "set" it for full output you lose all of it's automation so to speak.
 

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Assuming a good spectrum and somewhat even spread across the bottom, for a 40B you will want somewhere in the range of 4000 lumens to get around 70 PAR at the substrate (getting into the high light range). As Jeff said, there is a lot of variability with LEDs. so watts per gallon doesn't really work.

As one point of reference, the Current Satellite + Pro will put out about 70 PAR to the substrate in a 40B while drawing 45 watts, similar output to the Beamsworks output @ 72 watts. Unfortunately, it takes two of these to get even light across an 18" wide tank.

As another point of reference, I am running a custom LED that is about 85 watts total and gets to 130 PAR (measured) at the substrate in the corner (off axis from the light) of my 90P (same floor dimensions as 40B, but taller). I think it puts out about 7500 lumens, but that is only calculated, not measured. This is using some of the higher efficacy LEDs on the market, so much higher output than Beamsworks without a lot more power.

There are lots of variables . . .

-Justin
 
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