Re: Halide lamps and heat (SMTP Id#: 2935) - Reply

Jon Singer (
Mon, 31 Jan 94 13:08:12 PST

Rick Walker, in a recent post, says

"Every bit of energy you put in comes out as "light".
However, only a very small fraction of that "light" is
visible. Most of it is at such a long wavelength that
it is usually called "heat". (eg: blackbody radiation
at 2500-3500K)."

That's _almost_ true. A good deal of it also comes out as blackbody
radiation at a mere 350K or so, directly from the ballast & other
parts of the box. This is particularly true of things like halide
lamps, HPS lamps, etc., where the ballast may be only 80-95%

In general, though, Rick has it right: the wattage rating on a lamp is
how much it gets, not how much if gives off in light. As Rick points
out, regular lightbulbs are about 4% efficient in the visible range,
which means that a 100-W lightbulb would have to draw many thousands
of watts from the wall in order to actually produce 100 watts of

Another way you can verify this for yourself is that a 400-watt halide
lamp is MUCH brighter than 4 100-watt incandescent lamps. It is
therefore impossible for the "4 x 100 watts" or "400 watts" to refer to
the amount of light that comes out, because they'd have to be the
same. Right?

Someone else, I forget who, said something about "...edwardian...,"
referring to the display case that got us into this discussion in the
first place. I think that's actually "Wardian," named after a person.