Re: Light levels
Aquatic plants saturate their photosynthetic rates at between 300 and
1000 umol per m2 per second of Photosynthetically Active Radiation (PAR).
Anything below 100 umol/m2/s PAR should be considered low light as
aquatic plant light compensation points are in the range of 15 to 85
umol/m2/s PAR. Full sunlight on a cloudless, clear day at high noon in
the midwestern US is about 2000 umol/m2/s PAR. Thats about as precise as
you can get ... unfortunately, few people have acces to a quantum light
meter with underwater sensor. Next best is Lux which is lumens per m2. If
you know your lumen output and the surface area of your tank you can
estimate lux. Unfortunately, the amount of PAR delivered per lux changes
for different bulbs which produces a lack of precision. Finally, that
leaves us with Watts ... not very precise or informative, but certainly
adequate for most of us since most beginners realize from the 2 to 4 W
rule that they are woefully underlighted.
If you pack as much lighting as possible under your hood you will
approach the Ps saturation intensity (using fluorescent). Metal Halide
lights will of course provide even more.