I might be wrong here but dedoming a LED in a zoom setup is going to wast a lot of light. To my understanding the dome serves as a lens that bends the light and allows it to escape from the led die forward.
If only the directional part is being captured then the rest that hits he bazel is lost. In make perfect sens to dodome in a relfector. More of the light is bend by the reflector in to a beam with less flood.
Apparently there’s more going on here than that. It has been well confirmed that dedoming can give a very significant increase in throw even with aspheric lights. There was a thread last year either on BLF or CPF where the owner of OMG Lumens posted confirming it (his company makes the DEFT flashlights).
Obviously this wouldn’t be the case, if dedoming only increased the intensity of the light going to the sides and not the light forward into the lens.
I think the dome does two things:
(1) By changing the interface on the top of the die, more lumens are emitted instead of being refracted back into the die crystal. The result is overall lumens increase.
(2) It also enlarges the image of the die like a magnifying glass. Because the image is larger, the light is less concentrated… it’s harder to focus and has lower luminance…. so throw decreases.
I am not sure whether dedoming would change the light emitting angle, but I can be certain that dedoming increases throw due to the increased luminance of the die, not because of a less collimated light.
Imagine that you have a aspherical flashlight, say a UF T20. You can try to put a pre-collimation lens in between the aspherical lens and the LED. The result is you will see a larger projected die image BUT without any increment in throw. Yes, the pre-collimated lens will gather and direct more light into the aspherical lens so that they were not wasted inside the bezel, but this will only give you a higher OTF lumens NOT higher candela. It is the luminance which does the job to increase the throw (candela), not lumens to be exact.
Same goes to the LED dome. Again I don’t know if the dome is actually directing more light forward, but anyway the candela won’t be higher with a dome-on LED just because you think it should direct more light forward. The “larger” die image you see is just a perceived die size, I can simply put a 20mm pre-collimation lens in front of it and see an even much “larger” die size but that wouldn’t change the LED luminance and help in improving throw anyway.
Actually, my guess was that magnifying the image of the die with the dome actually decreases luminance, and thus reduces throw, because the lumens aren’t coming from such a concentrated area. I could be wrong though… I’m not a physicist.
Yes I understand what you mean and that is why I bring up the pre-collimation lens as an example. Of course the LED dome is not exactly a pre-collimation lens but the bigger die size you perceived with a domed LED can be related with the pre-collimation lens as well. I am neither expert nor physicist too and I found these out through reading in the forum and some simple experiments done by myself before.
Again you should check out DrJone’s thread in explaining the dedome and light emission behaviour.
This post has an excellent technical explanation about zoom vs reflector. Too bad the images are no longer available. Would any of you happen to still have the images?
Got caught in a barbed wire because focusing the beam also includes your field of vision. I can’t recommend it for people that does searching in the woods.
Never bought any zoomies after that.
Spill is very useful outdoors. It felt like a crime for me to use zoomies when I know that I need to see far but still aware of my surroundings at the same time.
Yeah, with zoomies you need to continuously adjust. For a walking light I tend to prefer a reflector thrower with a reasonably shallow reflector, so the spill extends to my feet without the spot getting too close to be blinding. Which is rare in top notch throwers of today as they tend to have reflectors just a bit too deep, so they are usable but uncomfortable in such setting.
