# Thread: LED Wattage / screen size calculation

1. ## LED Wattage / screen size calculation

I've read the excellent guide: Algae-Scrubber-Basics-The-Summary

Tank size: 30cm3
1 litre = 1000 cubic centimeters
1 US Gal = 3.78541 Litres
1 Inch = 5.08cm

((30*30)*30/1000)/3.78541=7.13 US Gal

1. Advice from guide is 1 watt per 1 gallon so it's more than sufficient to use a 10 watt LED as below? http://item.taobao.com/item.htm?id=10584760366

2. So my screen size should be;

2-inch^2 = 4
7.13-Gal * 4 = 28.52-area

ratio of L:W (2:3)

28.52 = 3x * 2x
6x^2 = 28.52
x^2 = 4.75
x = sqrt(4.75)
x = 2.1

L = 2 * 2.1 = 4.2-inch
W = 3 * 2.1 = 6.3-inch

L = 4.2 * 2.54 = 10-cm
W = 6.3 * 2.54 = 16-cm

correct?  Reply With Quote

2. Screens are now sized according to feeding, not water volume.

Info is outdated.  Reply With Quote

3. Also, your method of calculation is incorrect, I'm not sure where you are getting that but just start over.

1) old method: 1 sq in of screen per gallon. So for a 7 gallon tank, you need 7 sq in of screen

2) new method: 12 sq in of screen for each cube of food fed per day.

With either one, if you have a tank that small, I would think a 12 sq in screen would be more that adequate. In fact you might be best with the HOG .5 for that small of a tank.  Reply With Quote

4. Can see my math is wrong, it was late haha

Here's the math for single side screen;

7.13-Gal * 2 = 14.26-In2

ratio of L:W (2:3)

Area = 3x * 2x
6x^2 = 14.26
x^2 = 2.376
x = sqrt(2.376)
x = 1.54

L = 2 * 1.54 = 3.08-inch ( * 2.54 = 7.82 cm)
W = 3 * 1.54 = 4.62-inch ( * 2.54 = 11.73 cm)

and if I want it square;

L,W = sqrt(14.26) = 3.78-inch ( * 2.54 = 9.6 cm)

So has anyone experience with using the 10W LED?

Edit:

Also just to point out that the new method is quite close to that of the old for example;

L,W = sqrt(12) = 3.46-inch ( * 2.54 = 8.79 cm)  Reply With Quote

5. If you are planning a one-sided screen, then you need 24 square inches per food cube. Something close to 5" x 5" or 6" x 4".  Reply With Quote

6. Originally Posted by MorganAtlanta If you are planning a one-sided screen, then you need 24 square inches per food cube. Something close to 5" x 5" or 6" x 4".
Your correct or I feed them 1/2 cube per day... am not that mean.  Reply With Quote

7. Would like some feedback on a single 10W LED for this screen if anyone has tried before? Am probs going to take a shot at it given it's so cheap to try.  Reply With Quote

8. I think if you keep it 10 cm away from the screen, it might work.  Reply With Quote

9. That 10w light is WHITE light. Why not look for a 'Grow Light' that is red and blue? I would think they would be pretty easy to find in China as most of them are made there.  Reply With Quote

10. I recently purchased these:
http://www.aliexpress.com/snapshot/204087149.html

I went with 12:3 660 nm red, 450 blue

I was advised however growth outside the primary light area wouldnt be to great, so something like this would work for smaller screen,

They should arrive today and I will certainly let people know how they work! If you look around on ali baba there are several variants of lights, to many to pick from!  Reply With Quote