More light, less power - multiple emitters

[tylerdurden]

Now THAT is interesting. I think I have a picture in my head of what you're talking about. I'd love to see a sketch, if you can just get it onto a website it should be easy to post. The machining sounds difficult, but I guess it would be pretty easy for a CNC machine to handle. Would the emitters here be stacked slug-to-slug or dome-to-dome? In either case it sounds like they would need to be suspended in the middle of the refelector, as opposed to at the base or at the opening.

 

[phyhsuts]

This certainly is possible. The problem will be heat dissipation. The diodes will have to be back to back with the emitting sides facing away from each other. It will have to be in the reflector. Getting the heat out but not blocking the light will be difficult. Getting the focus right for both diodes is also going to be a pain.

 

[dukeleto]

OK, here is a rudimentary picture of what I described.
The bottom parabola (blue) is to scale, that's to say the HD is really placed at the focal point. For the 2nd parabola (red) I was too lazy, but it's not very hard to calculate; the actual equation of the curve will depend on the height of the heat sink.

Olivier

 

[tylerdurden]

That's what I had pictured, though I was thinking it would be longer rather than wider. OK, now build it! /ubbthreads/images/graemlins/smile.gif

 

[AilSnail]

vewwy nice. the light from the se would fill out the holes made from the lambertian and the heatsink fixture.

How about a pyramid shaped heatsink at the bottom, each topside has a led, and a petal-shaped reflector?

 

[evan9162]

AilSnail:

Good idea. I've been thinking about the best way to do this for quite a while.

You'd have to arrange your emitter direction and spacing such that the percentage of light gathered by each emitters reflector is MORE than the percentage of total light generated by the emitter.

Example:
If in the above configuration, due to the emitter not having a reflector surrounding it completely, each reflector only caught 20% of the emitters light, then the hotspot of the 3 petal configuration would only be marginally brighter than a single LED within one reflector that catches 50% of the single LED's light (the spill light would obviously be brighter). This is because with the single, you've put 50% of 1 LED into the projected beam - let's call that 0.5L. With the 3 and petal, you'd get 3 * (0.2L) = 0.6L in the beam.

With your configuration, the petals would have to be rather large. A better setup would be to angle the emitters to the side, or even slightly towards the back of the reflector, catching more light from each emitter (inverted truncated pyramodal heat sink block).

Someone could construct such a beast by mounting 3 or 4 emitters on a piece of square aluminum stalk, then cutting and merging 3 or 4 large (mag or whatnot) reflectors together. You would have to place the emitters such that they're at the focal point of their respective reflector. The resulting reflector profile might appear light a fat clover of sorts: 3 or 4 circles merging together. Might be an interesting experiment. Might be worth spending $12-$15 on mag reflectors.

 

[AilSnail]

evan, your statement about ponting the leds down instead of up might make sense. But, when you say 50% is gathered by a single led reflector and etc, remember that there is more light near the axis of the reflector. In fact, if one assumes a reflector with an aspect ratio 1:1, I think more light will be gathered from a sideward mounted led than from a forward mounted one.
If you point the leds more downward, more light will be reflected, but also the near-led-axis-light (the strongest light) will travel shorter before it hits the reflector.
I figure one could balance it off by pointing the leds further down when using shallower reflectors, and point them more upward (forward) when using deeper reflectors. This because the focal point of a shallower reflector is further away from the reflector bottom.

 

[chalo]

[ QUOTE ]
tylerdurden said:
Since LEDs are more efficient at lower power, we should be able to run two luxeons at, say, 200ma, and have the total light output be greater than a single emitter at 400ma.

[/ QUOTE ]

I have been working on a 2 x Luxeon III flashlight with side-by-side Stars. I originally chose two LEDs to make the neatest package with the rectangular battery I'm using. When I direct-drive a single 3W Star with that battery, I get 1300mA across the circuit. When I direct-drive two in parallel, I get 900mA total. (I assume this is intrinsic to the circuit rather than because of the extra test leads required to hook up 2 in parallel.)

When I look at the luminosity:current curve for the Lux III, it seems like I'll be making at least as much light from 450mA each through two Stars as I would from 1300mA pushed through just one. And the emitters should be much happier that way. And the battery will burn longer and recharge more times.

If I wanted to do a similar trick with a tubular flashlight, I would use multiple optical or reflective elements like Elektro Lumens' Tri-Star, rather than trying to make one reflector serve two sources.

Chalo Colina