[shalu]

Originally Posted by phkhgh

Shalu,

Do you have a correlation between the foot candles values and the common "Lumens" ratings that manufacturers supply?

read here:

Originally Posted by shalu

NOTE: you can NOT compare readings from bulbs of different sizes directly with this method, because larger bulbs has less surface intensity but compensate with larger area. Mathematically, I can integrate the intensity over the entire bulb surface(a simple cylinder in this case) to get the lumens output. I found that the Lumen numbers are in the same ball park of manufactor's published numbers, but always LOWER, by more than 50% in some cases. This is understandable: the light sensor is NOT infinitesimal and the bulb has curvature. The measurements favor the larger/flatter bulbs(T12), penalize the smaller bulbs(T6/T5). So again, don't try to compare the raw light readings between different bulb sizes in my results that will follow!

Originally Posted by phkhgh

Also, what's the difference, as far as plant growth, between 2 ODNO tubes, if they put out approx twice the light when OD at 4x, and 4 NO tubes run at their designed wattage.

Wouldn't the heat from the 2 OD bulbs (at 4x) be more than 4 bulbs running at normal wattage, even though total light output is presumeably the same?

If wattage consumption is the same, and the total light output is the same, then total heat loss is also the same: laws of thermal dynamics. You simply concentrate the heat loss from 4 bulbs to 2.

Do you want to do two setups to find out about the plant growth? I imagine growth will be the same. Except that with only two tubes, you can space them apart and apply individual high quality reflectors, which will make a HUGE difference in actual light getting into the tank, without even using more electricity.