Mission Impossible: 30g DIY led

[Constantine]

Hello planted tank community, first off id like to say how impressed I am by all of your tanks and your builds. I'm posting this thread concerning a diy led system for a 30 gallon tank. Its dimensions measure 30"x12"18"(w*l*h) and I was wondering if any of you could give me some pointers concerning how many cree 3w xpg r5 emitters I would need to sufficiently illuminate the tank. I'm planning on growing high light plants like glosso and dwarf hairgrass and the tank will be co2 injected with a pressurized system. I do not have a par meter or lux meter and my current lighting experience is limited to pc, t8's and t5's. I'm used to using the old watts per gallon rule and am a bit lost on calculating how many led's this tank would require to be sufficiently lit to allow high light plant growth.

My current build plan right now consists of (most from rapidled):
-Mean Well ELN-60-48P dimmable driver (several if needed)
-1.1" x 24" Aluminum Heatsink
-Some kind of fan and 12volt power supply
-CREE XP-G R5 Cool White 3W LED (unknown amount)

The way this lighting system will be mounted will vary from being right above the tank inside a wooden hood to being suspended above the tank. See pic attached. The stand will be custom designed depending on the lighting systems construction requirements.

[wastedtime]

Great Idea, How many LED's you need will depend on how high you hang the fixture above the tank and your optics, I would suggest 40 degree optics if you plan on hanging your fixture.

May i also suggest getting a wider heatsink and placing the LED's in a zig-zag pattern across the length of the strip. This will get you good coverage and less interference of the beams.

[GeToChKn]

The only problem with that is you're not going to know the height of your lights until you get it on your tank, with your particular plants and you can't adjust it with your current stand design.

Yes, X amount of lights will put out Y amount of par, but everyone's water is a bit different, CO2 amounts are slightly different and that will drive light position. I have a shop light above my tanks, no CO2, but I've adjusted my light position probably 5 times via chains it hangs on until I got the right amount of growing a bit of algae on the walls of the tank for the shrimp and growing algae all over my java moss. If your plants aren't big cover plants, you may need to raise it. Go with big cover plants, may need to lower it. There is no way to say put it at this height. It's a trial and error thing.

[Constantine]

The current image with the overhead open tank concept for mounting the led's has the emitters 28 inches up from the bottom of the tank and the leds are calculated to be using 30degree lenses. I'm just really confused on the intensity, do I go for coverage using multiple led's covering one area or do I use 1 led to cover one spot of the tank? I don't really care about some light spilling into the room. I used a triangle calculator and the Pythagorean theorem to calculate the necessary optics required for this configuration. It should be noted that Im placing the leds down the midpoint of the tank as illustrated in this image.

[Constantine]

Forgot and didn't want to ninja edit but the stands design is not set in stone because it hasn't been constructed as of yet. The top bar could be moved up higher and the heatsink and led contraption could be suspended via chains or wire and an umbilical could be made for the wiring for it with some shrink wrap.
The plant selection I'm looking at is pretty much the same as the one on my tanks page for my 17 gallon.

[wastedtime]

I would think that you should have some over-lapping where multiple LED beams intersect each other mid-way through the tank. Dont take my word for it, maybe some pros might chime in.

[Hoppy]

Most of the light from a LED is in the inside half of the cone. A 40 degree optic will put most of the light in the middle 20 degrees, a 60 degree in the middle 30 degrees. To get what you show would tank 60 degree optics. Here is a chart that may help you decide how many of what LEDs at what current to use: http://www.plantedtank.net/forums/di...ml#post1443426 You look up the lumen output vs current on the specs for the LEDs, which for Crees are pdfs.

[Constantine]

Originally Posted by Hoppy

Most of the light from a LED is in the inside half of the cone. A 40 degree optic will put most of the light in the middle 20 degrees, a 60 degree in the middle 30 degrees. To get what you show would tank 60 degree optics. Here is a chart that may help you decide how many of what LEDs at what current to use: http://www.plantedtank.net/forums/di...ml#post1443426 You look up the lumen output vs current on the specs for the LEDs, which for Crees are pdfs.

thank you hoppy

[Constantine]

Ok I used your chart hoppy and I'm not sure if I'm calculating this correctly also are you missing a variable for how many led's per row?

This is how I did it with the given equation of calculating par, I may have done it wrong because this seems like a super high amount of par but I don't know what this stands for? Is this for one led or a strip of them and if so how many of them?

[Hoppy]

Originally Posted by Constantine

Ok I used your chart hoppy and I'm not sure if I'm calculating this correctly also are you missing a variable for how many led's per row?

This is how I did it with the given equation of calculating par, I may have done it wrong because this seems like a super high amount of par but I don't know what this stands for? Is this for one led or a strip of them and if so how many of them?

L = the lumen output per LED at the current you will use.
n = the number of LEDs being used spaced at
a = distance between LEDs (inches) (in one or more rows, with the rows about the same "a" distance apart.)
H = distance from LEDs to the substrate (inches)
tan (...) is the square of the tangent of 1/4 of the optic cone angle

The equation gives an approximation of the PAR with all of the LEDs driven at the current which gives "L" lumens of light.

[Constantine]

You had n labelled as "number of rows of leds" that's why I was getting so confused.

[Hoppy]

Originally Posted by Constantine

You had n labelled as "number of rows of leds" that's why I was getting so confused.

Yes, I see that now. I need to go back and see where the mistake is.

EDIT: You are right. I just forgot what the "n" meant, so I have been using that chart wrong for several months

I have been wondering why more LEDs should give more PAR, since realizing that the light from distant LEDs has no effect at all on the PAR. Light barely penetrates the water surface when at a big angle to the surface, so LEDs at one end of the tank have no effect at the other end of the tank. "n" is the number of rows of LEDs, not the total number of LEDs.

[Constantine]

Ok here we go again and thank you for being so tolerant of the new guy. I'm pretty sure im still calculating this wrong but these are the figures I have. I'm just trying to get this right before I buy it because its going to be pretty expensive for my budget.

9 Cree XPG-R5's driven at 1250mA = 400 lumens per led
they are 28 inches from the bottom of the tank
led's placed approx 2 inches from each other
and the optics on the leds are 60 degrees

Now for the mad science.



edit: so its number of rows huh. Yeah 600 would be pretty bright... Like the freaking surface of the sun haha.

[Constantine]

Now I'm totally lost and confused haha. So how do I calculate the total number of leds required to illuminate the tank and how many led's are in one of those columns in the equation?

[Hoppy]

Originally Posted by Constantine

Now I'm totally lost and confused haha. So how do I calculate the total number of leds required to illuminate the tank and how many led's are in one of those columns in the equation?

The number of LEDs needed is the number that will cover the length of the tank, when spaced 2 inches apart. Your calculation was 9 times too high, if you have a single row of LEDs. So you get about 70 micromols of PAR instead of 625. 9 LEDs 2 inches apart makes about an 18 inch light. You would need 4 of those to cover the whole 72 inches of tank. At 25 inches from the substrate (you have 3 inches of substrate), the cone of light from a 60 degree optic will be 25 inches wide at the substrate and 10 inches wide at the top of the tank. Most of the light will be in the center 30 degrees of the optics, so the area of bright light will be about 12 inches wide at the substrate, but reflection off the glass will increase the intensity in the area outside of that. That should work fine.

You don't need to have LEDs all the way from end to end of the tank, since most of the light from the end LEDs would spill outside the end. If you stop about 6 inches from the end, you would need fewer LEDs, say 60/2, or 30 total, and if you do this with 4 separate lights, each would be 15 inches long, with about 7 LED on each one, for a total of 28 LEDs.