Just wanted opinions on whether this idea is worth pursuing. Elliptical reflector into a tapered light guide. The tapered light guide would generate something closer to a point source light and could also be used to achieve a desired focal point for the top fresnel, depending on the taper. The simplest way to build the light guide would be to carve 4 pieces of first surface mirror for minimal light loss. How efficient do you think this setup would be? 70-75%?? I did the best I could with the drawing but I don't know how accurate it is. It gives a general idea. I don't have any experience with this stuff. The only major drawback would be fitting the light guide. It would probably add 5-6 inches, if not more, to the size of the projector.
Gordon
Gordon
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quick experiment
I just ran an experiment using a cone made from >90% reflective aluminized mylar, as a tapered light guide. It does shrink the size of the light source, but it does it at the expense of the total amount of light coming out. And it gave me a pattern of light and dark rings that must correspond to zones that reflect n number of times before coming out. Considering how much loss occurs at each reflection, I guess this should be expected. I do observe a wide angle cone diverging from the pointy end of the cone, but the resulting light pattern is very ugly.
By the way, I think you can improve the efficiency of an elliptical reflector by adding another spherical reflector for the rays that miss the ellipse the first time. In the drawing below, the red curved lines are the spherical reflector. It send rays back through the arc, which will then end up at the second focal point (purple line).
I just ran an experiment using a cone made from >90% reflective aluminized mylar, as a tapered light guide. It does shrink the size of the light source, but it does it at the expense of the total amount of light coming out. And it gave me a pattern of light and dark rings that must correspond to zones that reflect n number of times before coming out. Considering how much loss occurs at each reflection, I guess this should be expected. I do observe a wide angle cone diverging from the pointy end of the cone, but the resulting light pattern is very ugly.
By the way, I think you can improve the efficiency of an elliptical reflector by adding another spherical reflector for the rays that miss the ellipse the first time. In the drawing below, the red curved lines are the spherical reflector. It send rays back through the arc, which will then end up at the second focal point (purple line).
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Oh well... it was worth a try.
The purpose is an attempt to generate a point source light.
Guy,
Thanks for the input. The spherical relector to recycle light is a great idea. But from some reading, it is my understanding that the problem with an elliptical reflector using a large arc light source, the converging light doesn't come to a point at the second focal point. The arc would generate multiple focal points. I don't know how this would affect things. I'd really like to experiment with an elliptical reflector though, if I can get a decent one cheap.
Gordon
The purpose is an attempt to generate a point source light.
Guy,
Thanks for the input. The spherical relector to recycle light is a great idea. But from some reading, it is my understanding that the problem with an elliptical reflector using a large arc light source, the converging light doesn't come to a point at the second focal point. The arc would generate multiple focal points. I don't know how this would affect things. I'd really like to experiment with an elliptical reflector though, if I can get a decent one cheap.
Gordon
point of elliptical reflector
I agree that the light from a non-point arc will not reach the second focal point of the reflector. But the elliptical + spherical reflector will at least get all of the light together in one area, going in the same converging cone.
I think the cone of light would have a bright uniform center, with progressivly weaker light toward the outer edges. Then some lenses could be used to project a very small image of the light cone a few inches away. This image could be spread with a negative lens to fill the lower fresnel with an almost point source light. But that's just an idea...
I agree that the light from a non-point arc will not reach the second focal point of the reflector. But the elliptical + spherical reflector will at least get all of the light together in one area, going in the same converging cone.
I think the cone of light would have a bright uniform center, with progressivly weaker light toward the outer edges. Then some lenses could be used to project a very small image of the light cone a few inches away. This image could be spread with a negative lens to fill the lower fresnel with an almost point source light. But that's just an idea...
I've just been putting a little more thought into recycling the non-reflected light when using the elliptical reflector and the actual efficency of an elliptical reflector. We all seem to neglect the fact that there is a big hole in the reflector, for the bulb to come through, that won't be reflecting any light. 89mm reflector diameter and 22mm hole for bulb(Edmund Optics). I'm starting to think that the elliptical reflector wouldn't be much better than Ace's setup, with a spherical reflector, that can work at 60% efficiency.
I drew the diagram with same dimensions(height and diameter) as the cold reflector offered by Edmunds Optics.
I drew the diagram with same dimensions(height and diameter) as the cold reflector offered by Edmunds Optics.
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Ellipse + hyperbola
I like the idea.
I would think sending ~40% of the light back though the arc wouldn't help. The intensity and heat at the base of the bulb would be high. Most light hitting the socket is going nowhere useful after.
I would think you have to figure some shape such that it hits the bottom reflector at a point such that it goes to the top portion of the reflector and to the second focus. Probably a weak hyperbola.
That would likely be beyond the DIY community.
I like the idea.
I would think sending ~40% of the light back though the arc wouldn't help. The intensity and heat at the base of the bulb would be high. Most light hitting the socket is going nowhere useful after.
I would think you have to figure some shape such that it hits the bottom reflector at a point such that it goes to the top portion of the reflector and to the second focus. Probably a weak hyperbola.
That would likely be beyond the DIY community.
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