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.
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.
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? :-)
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.
Yes.
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.
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.
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 range.
One 250W MH lamp is unlikely to produce as much light a eight 32W (T8) or *good* 40W fluorescent lamps. It will produce more light than 8 crappy fluorescent "shop lite" bulbs.
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 downwards.
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 course.
Yes.
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.
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!
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