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· Registered
204 Posts
Discussion Starter · #1 ·
Hi guys,

Just wanted to share with you and ask for your thoughts. I saw this formula in one of the Dutch sites and thought it was a good start in calculating for minimum light wattage requirements. I forgot exactly where I saw it but here goes the calculation:

L x W (in dm) + 20% of (L x W) for every inch of H.

Ex. Let's say you have a 16" cube. 1" is roughly 2.5 cm or .25 dm.
Your L in dm = 4
Your W in dm = 4
Your Height in dm = 4

Total min. wattage requirments is:
= (4x4) + (3.2* x 4)
= 16w + 12.8w
= 28.8w

*3.2 was derived from 20% of (4x4)

Sounds about right. I was told an average of 1.5 watts/gallon for plants. So that example is a 17G tank with 28W lights would be 1.6W/Gal.

· Registered
1,915 Posts
It's a good start but what type of lighting was it developed for? The problem basing lighting on wattage is that different types of light produce vastly different amounts of photosynthetically useable light on a per watt basis. For example, I compared a 96w CF bulb with 120w of convential flourescent tubes (4x30w) and measured that the single CF bulb produced 10X as much photosynthetically active photon flux density as the 4 conventional tubes totalling 120w.
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