MH bulb with Enclosed Luminaires - What do you think?

[zardoz]

Well I had a bright idea..I tried it...just hand holding the gear. But the results look very promising. Other than the fact I dont know for a fact where F2 is... Optics will be my struggle in this project I think. Not my strong suit...so I guess I gotta crack a couple of books .

zardoz

[ywh]

the reflector

using spherical reflector to reflect back the light to the lamp, not Paraboloid Ellipsoid or Cone

this is my friend's:

http://photos.gznet.com/photos/10136...jRoQMJQe2qazsk!RZmrALtw6kK.JPG

http://photos.gznet.com/photos/10136...nadrM1FczI.JPG

[rajkumar]

ywh:

The second link with a picture of double ended bulb with a reflector at the bottom is what I have in my EIKI overhead projector and it looks like "parabolic". I think it works pretty well with the halogen bulb I have in overhead projector. As soon as I get my metal halide lamp - I have posted picture earlier in this thread (150W cap style single ended made by GE) - I will try using that with the OHP reflector (parabolic shape). The dimensions seems to be pretty much similar and I dont think of any reason why it should not work.

By the way, I liked your posting and results. Keep on sharing the info and outcome on various aspects. I am glad you can find things in local market. And dont worry about your English! I lived in China (Shanghai - East China Normal University) as an exchange student for a year and liked travelling around. Most of my vacation time was spent in YenCheng (wetland - marshland) watching Migratory birds.

[Rolm]

ywh -

Yes, that little reflector back there could be spherical. The advantage there is that the diameter of the reflector is quite small. If I'm not mistaken, that's an "atmospheric" or "condenser" lens that is placed in front of it, for the purposes of spreading out the beam.

For that setup, a spherical reflector works quite well, because you have a very small light source (HQI bulb): approximately 1/2" (~12mm) in diameter. We are dealing with bulbs that are 4-1/2" (~115mm) in diameter, so we end up needing very large reflectors. If the size of a spherical reflector exceeds the diagonal measurement of the LCD, then we're wasting light, since a spherical reflector throws a parallel beam.

Another difference btw your example and what we've been talking about is that what you're showing is an "open" element setup, and we've been discussing "closed" elements, where the reflector encloses the bulb on all sides but one.

That being said, I've seen the pictures of your setup, and I'm jealous: I hope I can get results half as good as yours.

[rajkumar]

zardoz:

As rolm said, only elliptical reflector is designed for an end cap with a small apparture. The function of an elliptical reflector is to "collect" light for a point source lamp (F1) and point it to another focal point (F2) where its even and can be redirected to the LCD panel to illuminate the panel evenly. If you read this thread we have pretty good discussion on how this thing works.

I have put a great deal of time reading and thinking about various ways to work with light in the projector set up and IMHO elliptical reflector is probably the best way to avoide potential hotspot and use all the light from the lamp efficiently.

The reflector I have is made for theater lights and landscape lights using metal halide lamps up to 400 W. To find out F1 and F2 in a true or reasonably elliptical reflector should not be an issue. I have done it using an LED light but you can also use meglight with the top reflector part off - jsut the bulb on top and try sliding it back and forth in the reflector from the bottom and observe the beam behavior.

[zardoz]

I finally got my hands on a true "eliptical" reflector. Huge differance! Looks like I totalled 2 perfectly good SST bowls for nothing
Oh well all in the spirit of DIY. This one is alluminum but is painted white, do you think I should chemically strip the paint and pollish it? I'm sure I can get it VERY shiny. It's a prety big reflector, but I can deal with that.

zardoz

[Rolm]

You could strip & paint, or you could get some reflective mylar film and glue it to the inside. That should give you an easy mirror finish, as long as you get it nice and flat.

So where'd you get the elliptical reflector?

[zardoz]

I got this one from the local building wrecker, it had a 250 watt ballast attached to it. $75.00. I asked if I could buy just the reflector..offered the guy 30 bucks for it..he sold it to me for 25 plus a couple of Sylvania bulbs..total bill 32 bucks and change. I think I like the Sylvania's much better than the GE's I've been experimenting with. The quallity of light seems superior.

zardoz

[Rolm]

Yeah, the first GE I got was chipped, which I didn't notice until it blew up. I'm now using a Philips, which some ppl don't like, but I've had no complaints.

A building wrecker, eh? I may have to see if I can find one around here...

[ywh]

rajkumar:
welcome to YenCheng again! I live in YenCheng ( guangzhou )
you will to see anything at my overhead projector ,you well to get anything.double ended bulb ,reflector.

"The dimensions seems to be pretty much similar and I dont think of any reason why it should not work."
I don't know what are you talking about

The firster link is