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The size of the 40B almost requires two light fixtures to cover the 18" depth. I've also raised the single fixture in order to center it, but don't care for the glare it creates above. I'm low tech for now (but want the right equipment for CO2 if I choose that route) and my plants seem okay (slow growth, but look healthy). I'm avoiding the difficult plants until I know what I'm doing, but unsure how long it takes for a plant to respond to unfavorable conditions.


So two questions:
1) How do I know the best height for this light (Tank level 15"or is higher better)?
2) If I added a second fixture, is it overkill? I can dial down the intensity.
 

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I have a 48 inch sat. pro on my 50 gal. and it's about 16 inches from substrate and I have to dial it down to around 65 percent. Yes you can dial down the intensity.
 

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The size of the 40B almost requires two light fixtures to cover the 18" depth. I've also raised the single fixture in order to center it, but don't care for the glare it creates above. I'm low tech for now (but want the right equipment for CO2 if I choose that route) and my plants seem okay (slow growth, but look healthy). I'm avoiding the difficult plants until I know what I'm doing, but unsure how long it takes for a plant to respond to unfavorable conditions.


So two questions:
1) How do I know the best height for this light (Tank level 15"or is higher better)?
2) If I added a second fixture, is it overkill? I can dial down the intensity.
Using simple math and knowing the LED beam angle and distance from one row to the next (n/a for single row fixtures like the pro) will give you an idea of coverage..
tan 60 degrees = 1.732
x2 to crate the cone diameter = 3.46 cone at 1 inch from the light

to cover, say, 18" f/b AT the water line..
1/3.46 = x/18 = 5.2"

That will give you full coverage t/b f/b but not "even" coverage..
LED light cones are really concentrated more to the central area..

So light will be sig. less at the f/b edges for a inch or so (6.2" in this example) , till it sort of "catches up"..

Of course you need to apply reality to this theoretical..
In the 40 case, start around 7" from the water line, adj. accordingly.

Caculate PAR at the actual height from light to substrate..

15 + 7 approx.. =23"

SOOO roughly 30-40PAR at the substrate level for one PRO on full..
 
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I have a single Sat+ Pro on my 40b and it is quite efficient. I have no experimented with hanging the light, I simply have it sitting centered on my tank. The only downfall is that the top 3" or so of the tank in the rear isn't completely illuminated...somewhat shaded. The light at 100% is absurdly strong, and has zero issue growing demanding plants.

That said, I don't think you'll be able to run two at max, but definitely would be a good option setting both in the neighborhood of 40%. You'll have amazing coverage and the ability to grow just about anything you want assuming you're dosing Co2 and ferts!
 
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