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Re: metal halide lumen ratings

The reef keepers appear to be moving away from using lumen output to
compare lights.  Apparently lumen measurements are weighted to the response
of the human eye.  PAR (Photosynthetic Active Radiation, if I recall
correctly) measurements are weighted toward the response of plants and
other photosynthetic organisms.

For a detailed discussion of PAR and the PAR ratings of various metal
halide bulbs check out back issues of Aquarium Frontiers for articles by
Dana Riddle and others.  Dana Riddle's book entitled The Captive Reef
contains alot of PAR data for a large number of metal halide bulbs.  I also
believe that it contains PAR data for fluorescent bulbs, but probably not
T8 types.

If you have access to Compuserve there is considerable discussion on PAR in
the Advanced Reef Keeping section.  The archives contain alot of data and
discussion on metal halide lighting and the PAR concept.