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.
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.
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.
Internally, all they have is a multitap transformer and a capacitor.
Any thoughts on this?
They do not work well with the bulb straight up ( base down) and the light
deteriorates with age and usage.You should have about the same as 1000 watt
incandesant bulb for a mid life MH bulb of 250 watts.
There are two basic types, coated and clear. Color temp varies a bit
between the two, about 200 Kelvin, in the 4000 range. The bulbs are
designed to work vertically, base up OR base down, OR horzontally. Be sure
to get the right one for your fixture. Prices start at around $17 and go
up. Retail on some is over $100. Lycos search.
Not too far off. It might get a little better, but I wonder if you may
not have the highest quality lamp and therefore less than ideal efficiency.
Also note that it does take a long time to warm up fully and produce full
light. Also the color of the light may make it appear to be less bright
than it really is. However what good is light you don't really see? :-)
Eight 4-foot fluorescents is usually nominally 256-320 watts, and
usually with some inverse relationship within this class between wattage
and efficiency in the 32-40 watt-per-4-foot-bulb range.
Eight 4-foot fluorescents of nominal wattage 32 to 40 watts apiece would
normally in good conditions produce close to as much light as a 250 watt
metal halide. Check out the lumen light output figures!
- Don Klipstein ( firstname.lastname@example.org)
Try to find a coated bulb that is designed for vertical base down
operation (VBU is common, HOR is common, I dunno about VBD in a 250W)
VBD is probably the worst orientation for a "Universal" MH lamp.
It sounds like you got a universal lamp with a clear envelope. It's
probably brighter than you think, but the shadows are harsher and trick
your eyes into thinking it's less bright. A coated lamp will help with
that. Try to get one with a color rating closer to 3000 kelvin.
The lamp will get brighter during the first 100 hours of use, then it
will start to dim slowly for then next 10000 or so hours until it fails.
You know, I may try another route, if you think that it is sensible. I
am considering to place the light with the base up and the bulb
horizontal and the light going down, however I would coat the clear
glass with some light diffusing coating.
Makes sense. I will look into that.
I see. It has probably seen quite a bit of use and I have no problem
buying new bulbs.
Thanks a lot.
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
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.
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
--<< Bruce >>--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
My arc tube resembles a kidney bean. I believe that these lights were
made for mounting with the base up, horizontal, and the light going
No, the problem is that the bulb broke in shipping and the bulb base
is firmly stuck in the socket. The seller already responded and is
willing to make it good.
Electrically, they are both wired for 240v right now, I may rewire
them for 120V.
They could be old indeed, they are pulls from a miniature golf
I have a glass shield that basically completely closed the fixture
box. It is as wide and long as the fixture itself.
Well, looks like the glass should take care of it.
Absolutely, but I think that I have what you are desribing. If the
bulb falls apart, no pieces would fall down.
Would you have any suggestions? I will appreciate that, thanks.
Metal Halide lamps were developed primarily for commercial applications.
The light color produced is in the blue green spectrum. If you want to get
better color using them you could mix their light with some low wattage
incandescent lamps which are in the red orange part of the spectrum. A
color meter would help you find a good balance.
The color rendering index of MH bulbs is inferior to good fluorescent
fixtures, lumen degradation over time is much greater, and lumen output per
watt is lower. The advantage is you have less fixtures for a given large
space. They will perform in very cold weather, so for unheated northern
shops MH might help. The other application might be right over a machine, to
achieve a higher localized intensity than fluorescent. Currently, gymnasiums
are being changed from MH to T5 or T8 high bay fixtures at a lower wattage
per foot and more natural light.
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