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(It's a low tech natural planted 2" substrate with tannin colored water from Indian almond leaves and a glass lid for reference)

But after reading a colossal amount of stuff on light and lightening and then looking at the specifics of these lights I am looking for some input in what I think I have come up with.

Now price is always a factor but I'm ignoring it because it's only a factor for us as individuals and we can do that after everything else.

Let me start off with the specifics of the Finnex Stingray lights from their site:

48" 56x 7k white leds, 8-red, 8-blue

36" 40x 7k white, 8-red, 8-blue

30" 32x 7k white, 8-red, 8-blue

24" 27x 7k white, 5-red, 4-blue

20" 23x 7k white, 5-red, 4-blue

16" 20x 7k white, 4-red, 4-blue

12" 12x 7k white, 3-red, 3-blue

So looking at the white leds first what I did was figure out the comparative white lighting based on a per inch of fixture.

48" @ 56x7000 = 392,000 / 48 = 8,167k per inch

36" @ 40x7000 = 280,000 / 36 = 7,778k per inch

30" @ 32x7000 = 224,000 / 30 = 7,467k per inch

24" @ 27x7000 = 189,000 / 24 = 7,875k per inch

20" @ 23x7000 = 161,000 / 20 = 8,050k per inch

16" @ 20x7000 = 140,000 / 16 = 8,750k per inch

12" @ 12x7000 = 84,000 / 12 = 7,000k per inch

Now that's less then half the puzzle but it's solid start. Next I added in the comparative amount of red and blue leds. (Now I know this gets complicated because of things like red light depth penetration verse blue light and the equivalent kelvin of each to produce a overall PAR...never mind PUR), But keeping it overly simplified if we just compare the total number of leds to the % of red and blue it highlights more then I would have thought.

48" @ 72 leds with 8-red & 8-blue = 22.2% of leds R+B

36" @ 56 leds with 8-red & 8-blue = 28.6% of leds R+B

30" @ 48 leds, 8-red, 8-blue = 33.3% of leds R+B

24" @ 36 leds, 5-red, 4-blue = 25% of leds R+B

20" @ 32 leds, 5-red, 4-blue = 28.1% of leds R+B

16" @ 28 leds, 4-red, 4-blue = 28.6% of leds R+B

12" @ 18 leds, 3-red, 3-blue = 33.3% of leds R+B

Now with both these basic sets of comparisons it should become obvious why that Finnex PAR diagram we've all seen showing a graduated depth of 24" cannot really accurate for anything other then the specific light for the demo tank it was used on (if that).

Also it seems that that best combination of Red to Blue light for

*proper*wavelength leds is 2-1...so ideally you want 2x as many red leds as you do blue...and both of those should be less than 1/3 combined of your total Kelvin. We can discount that for this comparison simply because we are dealing with set fixtures.

But for those of us trying to do a "best guess" as to what actually works this is a summary I think will help.

*48" has 8,166k per inch white and 22.2% Red + Blue component*

36" has 7,778k per inch white and 28.6% R+B component

30" has 7,467k per inch white and 33.3% R+B

24" has 7,875k per inch white and 25% R+B

20" has 8,050k per inch and 28.1% R+B

16" has 8,750k per inch and 28.6% R+B

12" has 7,000k per inch and 33.3% R+B36" has 7,778k per inch white and 28.6% R+B component

30" has 7,467k per inch white and 33.3% R+B

24" has 7,875k per inch white and 25% R+B

20" has 8,050k per inch and 28.1% R+B

16" has 8,750k per inch and 28.6% R+B

12" has 7,000k per inch and 33.3% R+B

So looking at that the 16" will push a lot more light down deep compared to a 12"...in fact the 16" will push more light down then all the others.

The 12" at only 7k and with 33% R+B means it is going to be a much "warmer" light compared to the "colder" light of the 48" with only 22% R+B.

Now in my specific case I'm trying to light a 48x12x13h natural low-tech planted tank (33-Long). What most would say is pretty easy drop a 48" fixture on it...except now looking at what I just summarized there are 3 very different options.

(1x) 48" @ 8,166k per inch white and 22.2% Red + Blue

(2x) 24" @ 7,875k per inch white and 25% R+B

(4x) 12" @ 7,000k per inch and 33.3% R+B

The answer to deeper tanks has always been to push more K and even Blue to get the light down there but when it comes to shallower tanks (10g, longs, breeders) that extra light is not what you want (ignoring CO2).

And again cost aside there is one other added benefit to running multiple lights like these on shallower tanks. You can space the timers 1-hour apart with 11-hour "on" giving you 1hr morning, 10-both, 1-hour evening cycles.

For me...I think I'm going to go with 2x 24" because I'm a tad worried 33% R+B is overkill and I will take those 2 extra red leds instead of whites in the 48"

As for my basic guide to Finnex Stingrays...what do you think?