I can't find a good hemispherical reflector anywhere.

I've been wondering if anyone has tried enclosing the bulb in mirrors, with either a small aperture on the side facing the LCD or a lens of some sort, like this:
Click to view attachment

It's cheap and simple. Heat would be a concern but I'm sure an extra fan would be worth 2x the light.

You can try it and see if it is any brigher, but others have posted that idea in the past only to be told it will not work as well as you think. The reason being that each time light get reflected, some gets lost or eaten up by the reflecting material. I think the best thing is the spherical reflector for a fresnel, it would be cool if it stretched over the lamp, somewhat becoming close to your idea but the fresnel would still see the entire arc.

I'd like to hear from those people.

I just want to add 3 things:

1) I love that diagram!

2) Build it and see what happens.

3) If you can manage it, use first-surface mirrors to line your box.

I agree. If you put the Sun in there heat could be a problem. But test it and see what happens first .

As a rough guide, you can cut that opening about the same diameter as the projection lens, and likely still project the light from the edges. Even though it has a couple likely fatal inefficiencies, I think it would be neat to actually see what that thing can do. It's a bugger to accurately predict that sort of thing.

One of the problems is that light would have to bounce around so many times before actually making it out that hole, losing maybe 10% of its light for each bounce (but possibly as little as 2%). The reduction is compounded so it's not that bad. The other problem is that the Fresnel still only represents a fairly small area of where the light will actually project out of the box. And another is that the bulb will be intercepting a lot of the reflected light.

i think its worth a shot, but you would need a "collector" to capture this light and channel it to the lcd, like a focused beam.

Well...



Not a lot comming out of that box

That's probably why an ellipisoidal shape will work better, but he can try and see what happens, you never really know.

speaking of which and along these same lines..... how....ummm... accurate(?) of an ellipsoid would it have to be to be better than an ikea reflector? I mean, instead of making a box as outlined above, why not try to make a pseudo ellipsoid? glass would be to hard to cut and paste together, but I've seen ellipsoidal reflectors(stage lighting) that are not smooth interiors(the reflecting surface) but are "faceted" and wonder about someone putting one together from hexagons of wood or metal...(or triangles or pentagons) ...? has anyone who has access to a lathe or CNC machine ever actually tried to make an ellipsoidal reflector for one of the 400 watt bulbs?, and maybe just cover it with foil or something just to see? and yes, heat would be a killer..but again, unless you try it sometimes, you just never know....
edit: I think an ellipsoidal gathers about twice as much light as a spherical(well, in the vicinity anyway 40(spherical) to 75%(ellipsoidal) ?) but if we could build an ellipsoidal that was even 30% better than a ikea, hey, 30% is a lot of extra light....

and on that same subject, what is the minimum ellipsoidal reflector you need? like the ikea is only a small portion of a hemisphere but basically it does almost as much as a fullsized hemisphere, so is there a comparable thing in ellipsoidals?

I need that raytracing program. Is it freeware? I'm trying now3d and blender and I have no clue how to operate either of them.

It occurs to me that the closer the reflector is to a sphere, the better it would perform. So rather than 6 pieces of glass maybe I could use 7. I think i saw someone with designs for some sort of crazy toroidal shaped reflector, which I guess is similar to this. I guess that didn't pan out.

But I think where this differs is in the aperture. It should either be .25" in size, or be a fresnel of similar size to the collimizing lens with the light and focal point of the respective fresnels properly placed like so:

Click to view attachment

Raytrace them.

I'm thinking even with the best optics, there is still wasted light from the envelope being so large... Is anyone nearsighted? take off your glasses and look through a tiny (.5mm) hole.