And would have made the spot much larger. How much of the reflector is “filled” doesn’t really matter (but the distribution for any direction does).
The intensity on target equals the intensity of the bare emitter times the frontal area of reflector filled, then divided by the light-emitting area of the LED. So how much of the reflector is filled does very much matter. Cover half of your reflector and see if you still get the same intensity!
Up to a certain point of emitter size, the hotspot would actually not increase much in size, and just become brighter. Suppose you have disks of radius 1 and 3 (representing the hotspots from a smooth reflector), and you apply a uniform blur (OP texture) of radius 10. Then the resulting hotspots have radii 11 and 13; assuming the starting emitters have equal intensity, the larger emitter gives a hotspot that is 9x(11/13)^2=6.44 times more intense. Even if you use a larger emitter that has half of the intensity of the smaller emitter, the resulting beam is still more than 3 times more intense.
I understand what you mean. The OP reflector is like a Gaussian filter by varying the angle, distributing the light. A larger LES results in a larger spot, the effect of the OP reflector gets smaller because it describes the same filter with a specific radius.
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Now I’m curious why a SFT40 will out throw the SBT90.2 for the same reflector:
The SFT40 has an emitter area of 4,02mm^2 and 1800 lumens, so l/a = 447,8.
SBT90.2 has an emitter area of 9mm^2 and about 4700 lumens, so l/a = 522,2.
I saw some tests for the L21B, and the SFT40 throws 1167m (1Lumen) and SBT90.2 1148m (PiercingTheDarkness).
What am I missing?
The SFT25R has incredible 1500/2= 750 l/a!
I think it’s just because the SFT40 is often driven harder than 1800lm; I’ve seen reviews of lights like L21B measuring as high as 2200lm, which updates the lm/mm^2 to 547.
Also, the SBT90.2 draws a ton of current near maximum, and most cells won’t be able to supply that for more than a few seconds–after the voltage sag (even without thermal stepdown) a decent fraction of turbo output is lost. Might not be visually significant, but enough to move its intensity ranking among the throwiest emitters.
If we look at theoretical maximum (5500lm for SBT90.2 and 2600lm for SFT40 based on djozz tests), we get 611 lm/mm^2 for SBT and 647 for SFT40. Thus it might be unsurprising that the SFT40 should be able to out-throw SBT90.2 at the same fraction of their maximum drive power.
Very nice to see a realistic number of 4700lm for the SBT90.2; some is driven to higher than that, but not by much. I’ve seen tons of manufacturers claiming 6500lm from this emitter, which is an outright lie.
We love the SFT25R! In theory the Osram W1 does 900lm/mm^2 and should out-throw the SFT25R by a decent margin, but this is not observed in practice. The larger die of the SFT25R is less sensitive to reflector/focusing imperfections.
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