This article is from the Aquaria: Plants FAQ, by multiple authors.
Metal Halide (MH) lights are most commonly seen illuminating football
fields, but are also used in our hobby by reefkeepers and die-hard
plant enthusiasts, who demand very high light intensity. The fixtures
cost significantly more than fluorescent (over $200 per fixture). The
bulbs last longer and provide more efficient and brighter illumination
than fluorescents (typically 175-250 watts per bulb), but generate an
appropriately higher level of heat as well. Some aquarists like the
sun-like shadow effects generated by MH bulbs.
 
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