MH bulb with Enclosed Luminaires - What do you think?

[rajkumar]

I forgot to include this in my last post..

The other idea I am pursuing (in the interim basis) is to use the following lamp by GE. Its rated for 1000 hours but comes to about 12 cents an hour (affordable for watching DVDs). What I liked about it is the dimensions. Its less than 2 inch tall and very narrow diameter. My other OHP (EIKI) has a small bowl shaped reflector (i think its parabolic) sitting at the bottom of OHP and the current halogen lamp is mounted in such a way that the light center of the bulb falls in the center of the reflector which bounces it upward on the fresnel. It seems like if I use this MH lamp I would be able to use all the existing set up without twiking too many things..The lumens are not that great but almost all the light will be used so worth giving a try. Also, the lamp is very small so I can use other types of readymade reflectors too.

The ballast type is M81 so I am searching for the ballast right now.

[rajkumar]

here is the attachement

[Rolm]

Now THAT'S the kind of bulb that I wish we could find, just in a higher wattage. One of my early ideas was to try to use a bi-pin MH lamp in a very small (~2" diam) conical reflector, possibly even cutting out the center bulb of an ENX projector bulb. I could never find them either cheap or of decent wattage. Which is a little odd, since they make 600w bi-pin halogens for use in stage lighting.

If you're considering this kind of bulb, you might want to look into PAR56 or PAR64 reflectors. PartsExpress sells just the reflectors with a bi-pin base (I believe it's G12, though), but it's a parabolic reflector rather than an elliptical. Perhaps with a little sleuthing you could turn up an ellipsoidal PAR56 reflector that would work.

I'm a little wary about the tiny-mirrors-glued-into-a-bowl idea. On the one hand, if you look at an ENX or FXL halogen projector lamp, that's exactly how the reflector is formed. On the other hand, it would be a heck of a lot of work, and if the mirrors are not small enough (or don't abut perfectly) you could end up with a faceted beam that would not serve your purpose (think lots and lots of hotspots). Someone on this board tried this approach a while ago, and abandoned it very quickly when they ascertained how much work was going to go into getting it just right.

If you were going to try something like this, I think I would try to find some highly reflective substance to paint the inside of the bowl with instead. Or try getting some tinfoil as flat and seamless as you can on the inside. Me personally, I plan to polish the aluminum reflector to a mirror finish, which takes a little time but yeilds the best results.

I don't mean to shoot you down, I'm just offering my opinion on it. It's more work that I think I would want to undertake, especially if there is an easier alternative out there somewhere.

[stinky]

I have used two florex lights like udovee and had some sucess with them. But I would like to make the image bright and not have to worry about using so tons of optics. I know that the Florex design works on just creats lots of light and letting it pass though the LCD.

I was thinking about making the lcd the only part where light could escape from my light/reflector. So far I have come up with this disign. I just ordered a 400w MH fixture and a high power fan for my set up.

[rajkumar]

What size LCD are you using? 5 inch or regular overhead panel (around 10 inch diagonal) - Just curious.

[stinky]

10.4 laptop screen, because of the nature of the laptop lcd it will allow the most light through the screen. It will be hooked up to a laptop that has a USB tv tuner witch allows an S-Video input as well as coxial cable.

[rajkumar]

Mirrors reflect light straight so may not be suitable for a point source light. When the light comes from a point source and needs to be equally distributed on a large surface (10 inch panel), you might be better off with a curved reflector of some sort.

Check out:

http://gwidijanto.fcpages.com/reflector.htm

[stinky]

I planned for that, I have a high quality glass fresnel lens from an over head projector to distribute the light.

[Rolm]

Fresnels don't just magically straighten out light that is not in a semi-coherent beam. First you should try to set up your light source to direct as much light as possible in one direction, and then put the fresnel in that path.

You never manage to capture 100% of the light. If you did, you would have, in effect, created a laser.

IMHO, the only flaw in your design is that you rely on the light source itself and two 45degree mirrors to direct light towards the fresnel. If you were to set up some sort of curved reflector (as we have been talking about), you would direct FAR more light than you will with flat mirrors placed at 45deg angles behind the light source.

Here's a really bad illustration of what I'm talking about:

<img src="http://members.cox.net/rolm/images/compare_reflectors.jpg">

[rajkumar]

I hate this people selling bulbs online.. They have fancy websites with all kinds of bulb listed with individual price. My order for the small 150 MH bulb directly from GE company has been cancelled this morning...They sale by case only. I think its better to call and talk to these online retailers first before placing online purchase order.

On a side note, I was looking into theater/stage light suppliers online they have decent zoomable spot/flood light set up with elliptical reflectors.

If I cant locate the GE bulb by the end of the day, i am going to buy a MH retrofit kit from hellolight with Iwasaki 250W lamp (6500K) ;

http://www.hellolights.com/25methalbalk.html

I like the idea electronic ballast and relatively small diameter of the tubular lamp - easy to fit in the reflector.