02-08-2010, 07:05 PM
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Don't get too concerned over wattage, remember, that is not an accurate indication of light intensity. Watts is just the measure of energy used by the tube to emit whatever light it emits. The lumen is the measurement of light intensity (output), and the lux represents one lumen falling on one square metre. The measurement of lumens is the key to intensity, and while I rarely have seen this given on tube packages I have seen the lux (Hagen/Nutrafin's -Glo series of tubes has a lux chart). Natural bright mid-day sunlight is approximately 70,000-80,000 lux, and tropical plants require between 300 and 6,000 lux depending upon species; crypts are at the 300 end.
As an example, I have T8 Life-Glo 2 tubes on my tanks, and their lux rating is 320. So with two of these, there is about 640 lux. However, a majority of plants will do fine under this, as my tanks and Angel's tanks and other people's tanks prove. When I tried the T5 HO tubes, same brand, the lux was close to 500 per tube, which is why I say that one 48-inch T5 HO puts out the intensity of 1.5 T8 tubes, and over the tank the brightness was significant.
The watt per gallon idea works quite well with standard T8 tubes, for a guide. But as soon as you get these newer tubes that are more intense [like the Zoo Med series of T8] or the T5 NO and HO tubes, the watts basically becomes meaningless.
Last edited by Byron; 02-08-2010 at 08:20 PM..