# How to calculate Light



## arulnathan

I have 36L x 15w x 20H inches...how much of watts do I require and how to calculate it.

Thanks!


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## xcooperx

You have 47 Gallons (176.98Liters), For High LIght you need to have atleast 145 watts of Lightning, 110 watts for medium and 96 watts for Low Light. I recommend compact lightning


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## hoppycalif

I would use about 3/4 of the watts Cooper recommended for each category. One thing for sure, there are no hard numbers for any of the lighting categories, but if you start looking at 2 watts per gallon you can adjust upwards for high light and downwards for low light.


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## havoc1995

It depends on what you grow... but I would say if you have 130W you would be good to go.


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## ruki

Unfortunately, there isn't an easy absolute answer for this question, for many reasons...

If you are new to this, the safe choice is to do the low-to-medium light and raise easy to grow plants. This way you have a nice looking tank with real plants with minimal effort and algae. 

As you increase the light levels, you have pay much more attention to nutrient levels, otherwise odds are you will get an algae farm instead of a nice looking tank. (Been there, done that  )

Watts per gallon is a very rough estimate perhaps as bad as +/- 80 percent. 2 watts per gallon (+/- 30 percent) from an aquarium fluorescent plant bulb and fixture with a decent reflector gives the sage choice of medium light as HoppyCA suggested. 

The +/- variation comes from

(1) Electrical efficiencies of the different tube types. Thinner tubes are generally more efficient than thicker tubes. The more efficient the tube, the more light you get with the same watts/gallon.

(2) How good the reflector is. Linear tubes (without bends) can have better reflectors. Thinner linear tubes require much less space and materials (i.e. cheaper) to make good reflectors for, so these fixtures generally have better reflectors than those for thicker tubes. The better the reflector the more watts/gallon actually gets sent down into the tank.

(3) How much light useful to plants the tube produces. Plants like particular blue and red colors. Tubes made for human eyes don't produce much light useful for intense plant growth. Plant bulbs are really good for this, but look dim to human eyes, so you want some colors for the plants and some colors for us to view the aquarium.


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## arulnathan

Thank u all for helping me....I changed my aquarium to 36Lx20hx18w and wanted farmula to calculate the WPG.


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## czado

If you wanted to get straight watts per gallon, it would be

Length inches * Width inches * Height inches / 231 = Tank Gallons
Watts / Gallons = WPG

(and Gallons * WPG you want = Watts you need for that WPG.)

If you want to use an alternative, this one gives you some ball park figures.


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## arulnathan

Thank you all once again for the help.

Nathan


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## ruki

czado said:


> If you want to use an alternative, this one gives you some ball park figures.


I like this one. Now they just have to add T5, T5HO and PAR and I'd be in heaven


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## czado

T5 and T5HO isn't on his PHP app, but is in this MS Excel compatiable/O spreadsheet if you'd like. "Eq T12 wpg" standardizes back to equivalent T12 watts/gallons, "Tong's wpg" standardizes back to the 55gal baseline in the article.


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## arulnathan

Hello all,

Yesterday on my 36Lx20hx18w tank I installed two 24 inches long tubelights, one with 18 watts daylight and another with 20 watts hitachi fluorescent tubes for Plants....this is very low light I know .....but would like to know will this do any good to my plants....as at present my hood can acomodate this much only. 

Thanks!
Nathan


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## czado

You might have some success with attaching stuff like Anubias, moss, and Java fern on vertical driftwood to keep them closer to the light. Your best bet are likely floating plants such as Anacharis, Hydrocotyle sp, and Hornwort. Otherwise its not very much light and it is doubtful you'll support many plants at the substrate depth. Perhaps Crypts are worth trying.

If you're interested in cheap alternatives, you should be able to add a dual 36" T8 fixture from the hardware store and DIY a reflector (such as a hood with an interior painted white) for solid "low light."


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## ruki

czado said:


> T5 and T5HO isn't on his PHP app, but is in this MS Excel compatiable/O spreadsheet if you'd like. "Eq T12 wpg" standardizes back to equivalent T12 watts/gallons, "Tong's wpg" standardizes back to the 55gal baseline in the article.


This pretty much what I wanted. A decent normalization.
Lumens/watt	Eq T12 watts
T12	58.9	1
T10	62.3	1.057724958
T8	91.1	1.546689304
T5	104	1.765704584
T5HO	92.6	1.572156197
MH	84.1	1.427843803
CF	79.4	1.348047538

I might re-normalize based upon T8 since that's what many DIYers are using for fixtures since tubes are very cheap.


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