Re: light on aquariums

["S. Hieber" <shieber at yahoo_com>]

RE art: Someone suggested this about lighting an aquarium:

> The most important thing is coverage. Get light into
> all of the nooks and crannies. 

When you plan the aquascape of your tank, you might want to consider
the visual effect of light(er) and dark(er) and plan on areas of less
light.  These is easier to due with more powerful and compact light
sources such as metal halides and power compact flourescents.


RE the technical:  I think someone said MH were incandescents.  Metal
Halides, like flourescents, are arc lamps, not incandescents like their
more common cousins, the quartz halogen lamps.  Although metal halides
have filament-type electrodes that heat up, as do many and the most
common flourescents, their light is caused by electrons arcing across a
mercury vapor, which gives off UV photons, which in turn, depending on
the coating (in florescents) and the gases in the bulb (in MHs)
generate other photons at lower light levels, in the visible and
infra-red range.  

Quartz Halogen bulbs, somethimes called Halogen, Quartz Iodide, Halogen
Iodide, etc. have tungsten filaments that get hot and emit light like
any other incandescent.  But the presence of a halogen gas causes the
filament particles (the filament slowly vaporizes from the heat) to
redeposit on the filament.  So halogen filaments last longer, so
halogens last longer than other incadescents.  And because the quartz
envelope becomes coated with filament particles (the blackening of the
bulb) more slowly, they are rated for more lumens per watt than other
incandescents.  But they ain't go nuttin on PC or MHs when it comes to
efficiency or lumens per watt.  Incadescents are efficient heaters, but
inefficient light sources, much less than 10% of ther energy is given
off as visible light.  And I thought some cars wasted energy! :-O 

Scott H.

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