Metal halide interior lighting

Anyone tried metal halide lighting for an office/study room?
My study gets a bit dreary sometimes - thankfully, there's a big window, but that doesn't help during Winter.
I've tried CFLs, they're OK, but a bit dreary. 'Daylight' simulation bulbs are nice, but way too dim, and v. expensive.
So, I was looking for something very bright, 'daylight' coloured, semi-energy efficient (i.e. no 500 W halogens) which would be nice for reading and computer use, and might help cheer me up through the long Winters.
I'd kind of settled on some metal halide uplighters, to provide some pools of semi-diffuse light in my work areas, as well as provide strong general illumination. However, I just wonder what people's experiences are.
I know modern linear fluorescents are very good, but can you get the same level of illumination/colour quality from them?
Is the uplighter idea going to cause devastating glare on computer screens?
Do MH lights flicker, and/or are electronic ballasts available/retrofittable?
Of course, there's the problem of how I attach industrial carved metal bricks to a stud partition wall, but I'm sure I could find a way.
M
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wrote:

The common fluorescent tube has a colour temperature of about 3-4,000degK which is a bit on the yellow side for many. You could try a 6,500 deg tube which will give a much "whiter" light. Osram 865 daylight is fairly common although may have to be ordered. http://www.lightbulbs-direct.com/variant_detail.asp?var042
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Peter Parry.
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It may just be you don't have enough light. Retrofit CFLs would not be what you would choose for a new design; to achieve the lighting levels you would expect in an office, you're going to be looking at more lighting than you could get from a reasonable number of retrofit CFLs. You are going to want a number of linear fluorescents in appropriate fittings. Office lighting levels generally need to be much higher than you would have anywhere in a house.

150W MH will be similar to a 500W halogen in light output. The next common size down is 70W, and up, 250W. They are available in colour temperatures from 2700K (same as filament lamps) to above 4000K, depending on each manufacturer's range. (Some special ones are available much higher -- I've got a 250W 10,000K one, but you seriously don't want to work in that colour temperature;-)

The light output is similar to a fluorescent of the same power (although efficiency improves further with the higher wattages which you probably don't want).

It works quite well, although probably not as well as purpose designed fluorescent luminaire reflectors in modular ceiling fluorescents.

Electronic ballasts are available, certainly for the 70W and 150W. Some manufacturers claim longer life on electronic ballasts, and for some higher quality MH lamps (such as Powerball), I think they almost insist on electronic ballasts if you want the lamps to meet life, lumen maintenance, and CRI maintenance specs.

? If you are making your own, beware that metal halide luminaires must be designed to contain the red hot fragments from an exploding lamp, as that's quite a common way for the lamp to let you know it's reached the end of its life.
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Andrew Gabriel
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Andrew Gabriel wrote:

I'm sure that's the bulk of the problem.
It's a relatively small room (only about 9x11 ft), a converted bedroom, and the single pendant lamp is desperately inadequate. I've certainly recognised the need for linear fluorescents, and plan on at least one double 5ft fitting.
I was really looking for something very bright. Certainly, with a nice double fluorescent over my desk, I would expect to get about 750 lux. Which is within the range of what is recommended for office lighting. But I was wondering whether it would be a viable project to get the lighting up to 'SAD' busting levels, which is supposed to need 2x-3x that. If I really did want to go for that level of illumination, then it would need a lot of fluorescents, in tightly packed formation.
What really inspired me was a visit to a university department which had outfitted their 'reading room' in this sort of way. Several very bright, daylight-simulation, metal halide uplighters. The room was absolutely fantastic to read in. However, one of the uplighter ballasts was making a terrific buzzing, which kind of put me off the idea. There were also no computers so I don't know if there would have been glare issues.

I'm sure you're right. I know everyone says you're supposed to have recessed fluorescents for VDUs, but I suppose surface mounted would do, and that's what I intend to get. No chance of recessing anything here - there's barely 5 cm in the void between ceiling and whatever solid thing is behind it.

Oh. I wasn't intending on making my own. I had got to the bit about exploding red hot bits and decided it would be a bad idea. My comments were in reference to the weight of the fittings - 5-6 kg for a wall mounted uplighter, which strikes me as quite a lot. More than I'd want to trust to spring toggles and plasterboard - and no the battens aren't anywhere close.
I had thought about experimenting with retrofitting a halogen floodlight - the lamp fittings are the same. In the end, I found that MH bulbs are a bit bigger and might foul the reflector. Then there is the issue of whether the wiring is insulated to the ignition voltage. And, of course the fact that budget halogen floodlights look hideous and spray out the light in totally the wrong direction.
Thanks for the input, it's been helpful. I may well abandon the MH idea, if some nice fluorescents do the job well. However, something in me still thinks they are cool and I might just end up buying one to experiment with :)
Regards,
Mark
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That's fine. You don't need to light the whole room to that level, but you don't want a large contrast between the brightest and darkest areas.
As a quick check in my garage, which has single bare 5' 58W tubes on 4' spacing... I get 550 lux at desk height under the end tubes, and 650 lux under the middle tube. Ceiling is white but walls are bare concrete blocks. In a room with light walls, you would do better, but in a luminare with a difuser, you will lose out there (and you probably don't want a reflector -- see below).
At this sort of lighting level, I would suggest tubes of 3500K to 4000K colour temperature.

Office lighting and SAD lighting are completely different, and largely at odds with each other. For SAD, you really need to be looking at the light itself or at least have it in your field of vision. For office lighting, you don't want this at all. I would not attempt to solve both with a single solution. I'll ignore the SAD issue here - come back if you want some advice on that.

Recessed or surface mount is largely irrelevant from the lighting point of view. Where you have an expanse of ceiling going off into the distance as in most open-plan offices, it's important the lights use reflectors which direct the light only downwards so distant lights which form a shallow angle with your horizon are not visible -- these would cause glare and reflections (although much less so with any modern monitor). In your home office, this glare/reflection issue is not relevant as the ceiling won't go off into the distance. Furthermore, you do actually want the lighting to spread sideways so the walls are illuminated (but not too brightly), so classic office/VDU downlighting isn't going to be so appropriate in a home sized room.
What would probably give the best lighting would be one or two bare tubes on the ceiling over your head, with lower powered supplementary more directional lighting providing in-fill for any areas this leaves too dark. You may quite reasonably not like the idea of bare tubes, in which case look for a fitting which gives a good light spread in all directions. You'll definately need two tubes if your fitting includes a diffuser, as diffusers are lossy.

That would account for a magnetic ballast.

70W might fit in some, but the 150W is about an inch in diameter. 250W has completely different end caps.

It's around 4kV, but MH lamps are not wired with special cable when remote from control gear, so it would appear to be OK. (Hot restrike MH lamps do require special cable, as they take a 25kV ignition pulse.)

Also need to be careful the reflector doesn't focus any of the light back on the arc tube. Whilst that's a good thing for a halogen lamp, it's a really bad thing for a metal halide lamp. They often use specular reflectors to avoid any chance of this.
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Andrew Gabriel
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mused:

I think someones confusing 'recessed' and 'category 2 louvres'. You can get surface or flush flourescents, with either plain, prismatic or the VDU friendly category 2 louvres. I've fitted plenty f each type here and there.

After reading this I think I might do the same, I'm not the only person to use my office but I'm the only one that wants decent lights in there. I'm also quite a miserable git so would benefit from from anything that combats SAD! Think I might grab a couple of metal halides to play with.
Thanks for the idea. ;)
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Stuart.
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I use a 300W linear tungsten halogen lamp above my workshop bench. It's like working in the sunshine in winter, but can be a bit hot in summer.
Nothing beats tungsten halogen for it's genuine full spectrum output.
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Clive Mitchell
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I'd go with linear fluorescent, lower cost, as effective, more flexible, and more reliable.
Choose you tubes wisely, see http://wiki.diyfaq.org.uk/index.php?title=Fluorescent_Lighting
NT
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