One Way to Design a Planted Tank LED Light

[Hoppy]

Doc7, you ask a number of good questions The equation that this method is based on was derived from data that I have from LED lights with rows of LEDs spaced about the same distance as the LED spacing. But, the maximum LED spacing I used was 3.25 inches max., and the number of rows was 3 maximum. Extrapolating from that will work, but probably not for 3X extrapolations. The higher above the substrate the light is, the more you can extrapolate, just because the cones of light get bigger as you go higher. (I think it is about the overlap of the light cones, more than anything else.)

I suspect that with 3 rows of LEDs, 20 inches from the substrate, and 60 degree optics, and 4-5 inch row spacing, you can use n=3. At 20 inches the center half of the cones of light is about 10 inches in diameter, so there is a lot of overlap of the rows of light. I'm not sure that with 40 degree optics you can use n=3, and I suspect you can't. But, for a 20 inch height I wouldn't use 40 degree optics anyway. A 40B tank is about 17 inches high, so, with 3 inches of substrate, the top of the tank is about 14 inches from the substrate, and a light 20 inches away is about 6 inches from the top of the tank. A 40 degree optic would give a circle of light about 4 inches in diameter at the water surface. These circles of light are very visible when they are that small, and wouldn't look good at all.

The PAR numbers you get with those spreadsheet calculation is for right under the middle of the light, so the distance between the outer rows isn't relevant. As with any aquarium light the PAR will drop off near the glass anyway - theoretically. But, light reflected off of the glass adds to the PAR near the glass, greatly reducing the drop off.

[j_r_smith]

This is some fantastic information. I have been trying to determine the correct number and type becuase I want to move away from t-5's. As I am reading this it seems to implicate a fixture made up of all white LED's. I have had many recommend a mix of cool white and blu or royal blue. Some at a 1 to 1 ratio and others at a 2 to 1 ratio. What are your thoughts on this? And does the calculation still work for the white only when doing a mix?

Thanks!
Joe

38Gal 30x12x19 planted tank
56Gallon 30x18x24 soon to be planted
95 gallon 36x24x25 soon to be planted discus.

[cheesehead]

Hoppy, thanks a lot for the work. I've been planning a LED build for my 200 gallon, full spectrum, and have pieced together a spreadsheet with spectral output of various LED's and what I'd need to have to get xxx illumination. I get numbers fairly close to yours for numbers of LED's.

I've got a question on the spreadsheet (ver 5), related to the half angle/full angle question stated earlier. The documentation says that if you don't use a lens for the LED's, that

Cone angles for bare LEDs, with no optics installed, XP-G, XM-L, XP-E use 70 degrees, XR-E use 50 degrees

When I look at the spec sheets those look like half of the full width half maximum (FWHM) for the bare LED's (for example, for the Cree XPG the spec sheet the spatial distribution is 50% of maximum at +/- 60 degrees, therefore 120 degree half maximum or FWHM).

So should the angles for the bare emitters be 140 (or 120) and 100? Or am I miscalculating what a "60 degree optic" is by assuming it's +/- 30 degrees at FWHM?

Thanks.

[dafil]

Hoppy,I am asking for your help and opinion-what PAR will get with these 14pcs 3x1w,60deg optics,28inch from substrate,270lm each bulb

[Hoppy]

How far apart, center to center, are the bulbs? I don't think my empirical equation will be very accurate for this type of setup, but it may be close enough to know if you have very high light or low light.

[dafil]

4 inch betwen the rows.3,5 inch center to center in the row.
10x

[Hoppy]

The calculator says about 30 micromols of PAR at 28 inches.

[skanderson]

im having trouble inputting figures into the spreadsheat. anyone have advice? im planning a led fixture for my new 300 cube build. 48x48x30. thinking of keeping the leds 48 over the substrate and using 30 degree lenses.

[makutaku]

Originally Posted by skanderson

im having trouble inputting figures into the spreadsheat. anyone have advice? im planning a led fixture for my new 300 cube build. 48x48x30. thinking of keeping the leds 48 over the substrate and using 30 degree lenses.

The calculator relates six variables. You provide five of them and it calculates the sixth.

You need to answer the following question: what do you want it to calculate ?

Then you need to provide data for all the other five variables. From your statement you already have:
LED height = 48
Cone angle = 30

If you can get the value of three more variables, the calculator will give you the value of the sixth.

[skanderson]

that isnt my problem, i have 5 of the variables but i cant get any variables entered into the calculator. any advice on how to put it into the spreadsheet or do i just need to do it by on paper.

[Hoppy]

Are you using The Excel spreadsheet program? If so, you should be able to enter values the way you would with any other spreadsheet.

[m00se]

Sounds like it's opening the spreadsheet in read only mode.

[skanderson]

that may be the problem. any way to change that? im not a tech person by any stretch of the imagination.

[skanderson]

i think it is because i dont have microsoft office installed does that sound right?

[Hoppy]

With a PC I think you do need to have Excel or Office installed to make the spreadsheet work. Without it, it is just a table in a document.