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RE: Metal Halide temperatures



If memory serves me, an average U.S. manufacture 175W Metal Halide produces
a surface temperature of approximately 475' F (that's four hundred and
seventy-five) on the surface of the outer envelope.  From GE's pages, the
250W max bulb temperature is 400' C (probably the surface of the inner
envelope-not detailed), while the max base temperature is 210' C.  Pretty
warm, and they do require some special handling.
The Metal Halide is an arcing bulb, with the arc contained inside a
synthetic quartz inner envelope (in most U.S. bulbs), which is in turn
protected by a u.v. blocking outer envelope.  You can be sure that if you
were to "touch" the outer envelope of a MH while it is in operation (or
shortly after it has been turned off-before cool-down), you would leave a
fingerprint.  Quite literally.  I learned from my friend's second degree
burns from "bumping the bulb" and use extra caution.  This is also why the
bulb must be protected from "splash-back" from your aquarium occupants-it
will quite literally explode ("pop", actually-it's pressurized) if much
water comes into contact with the hot outer surface.  When the outer
envelope fails the bulb shuts down, and cannot be restarted.  The
possibility of catastrophic failure (self-destruction) is why OSHA requires
a protective housing for these bulbs when used in work areas (to contain the
glass/quartz shards).
A standard measure of output is about 10,000 lumen for a 175W, roughly the
equivalent of five 48" fluorescent bulbs from a surface area (inner
envelope) of about 2.5 - 3 square inches-hence the concentration of heat
(ref earlier thread).
The inner envelope contains mercury and gas and poses a health risk, much
like fluorescent tubes, if you are exposed to the gas released from a
shattered bulb.
I have used MH systems for ten years now, and still have "mixed emotions"
about them.  Living in S. Arizona, my cooling bills for the house are pretty
high in the summer (especially when I was running 4-175W & 2-250W MH's on
the reef), and having to provide supplemental cooling to boot...well.  Now
the 225 is set up as a planted Discus aquarium, with only a pair of 175W
pendants and a pair of 72" VHO for supplemental lighting.  Still warm, but
the aquarium is stable at 89'F (not cooled, 79' ambient).  Fish and plants
are both happy with the results.
The biggest draw (aside from the biological benefits to the aquarium
occupants) is the intensity of the light produced.  The closest comparison
is snorkeling in shallow, very clear water-with the "sun-ripples"
throughout.
I hope this helps you in your research.
Links:
http://www.ge.com/index-java.htm (General Electric)
http://www.eye.co.jp/index.html (Iwasaki homepage/eye and ace series)
http://www.venturelighting.com*/ (Venture Lighting homepage)
aqualine-buschke is another good manufacturer (European fixtures and bulbs)

Ray Ulrich
rgulrich at flash_net
http://www.flash.net/~rgulrich