On Wed, 07 Dec 2005 14:45:44 GMT, Ignoramus8325
wrote:

I bought two used metal halide lights. They are about 1x2x0.5 feet in
size and take 250 watt bulbs.

I tried one of the two I bought (the second has a problem, likely due
to shipping, that I hope we can easily rectify with the seller). I
laid ot on the floor and directed the light at the ceiling.

Check the lamp before you do that - most MH lamps sold today are
"Universal burn" with a /U in the part number, and position is not an
issue. But there are still a few lamps out there that require a /BU
base up or /H horizontal, and they have keyed sockets and a pin on the
lamp base, so the lamp stops turning in the right position. The arc
tube in the horizontal position restricted lamps is curved like a
kidney bean, and it has to be vertical ^ .

Open the dead one and wiggle all the connections - it could be as
simple as a loose .250 tab connection on the ballast voltage taps. If
the top of the capacitor is bulging on the terminal end, it died - see
comment below.

My first impression is that, first, they take quite a while to warm up
(not a problem), and second, they are not that bright. I would say
that one 250W MH light makes about as much light as do my eight 4ft
fluorescent lights. Maybe it is more of an expectations issue and even
that is great.

Internally, all they have is a multitap transformer and a capacitor.

They could be really old lamps, the output fades over the 12K to 15K
hour lifetime. Or the lamp capacitors could be drying out and going
bad from general old age, takes a standard electrolytic motor run cap
of the right ratings. Costs you under $5 to fix that one.

WARNING: If these fixtures are used overhead and are the open
reflector style that don't have a completely enclosed reflector
housing and glass or acrylic lens, you MUST run the lamps with the
'double shield' inner guard over the arc tube. The guard looks like a
chunk of 1" x 3" Pyrex tube in brackets over the arc tube, inside the
lamp's outer envelope. (Probably because that's exactly what it is.)

When the arc tube reaches the end of life, they build up a lot
higher internal pressure when they reach operating temperature.
Usually they just crack the arc tube and quit, but about 5% of the
time it shatters with enough energy to break into shards, and
sometimes the chunks have enough energy to also shatter the lamp outer
envelope. After that, the laws of gravity take over...

If the light fixture doesn't have a tempered glass or heavy acrylic
lens that can catch all the hot bits that will escape, you /really/
don't want to be standing right under the fixture when this happens.

Secondly, the color from the bulb that was there, leaves much to be
desired, it is kind of "cold". I am curious if I can buy some other
250W MH bulbs that produce a more lively color.

Yes, there are higher color rendering lamps with a better mix of
metals in the arc tube, and with the 'deluxe white' coating on the
outer envelope to diffuse the light.

But they are pricier, too. Regular lamps are in the $20 to $40
range.

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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