I am guessing domed is better because I want most light hitting the lens.
What is the best?
De-domed decrease lumens but increase throw both reflectors and aspheric lenses.
Dedoming will:
1. Reduce total lumens usually around 15-20%. Flood mode is a little less bright.
2. Increase lux by as much as 100%. In spot mode, the spot is smaller than with the dome, but it’s much more intense and throws much further.
3. Shifts the tint around 1500 degrees warmer. Unfortunately, every XML2 I’ve tried to dedome has always gone somewhat green in addition to getting warmer. I’m still hunting for the perfect XML2 tint. Domed tints definitely look much prettier.
In addition, it is sometimes possible to get a wider angle of flood mode with a dedomed emitter. The key to getting widest possible flood is to mod the light so the lens retracts as close as possible to the top of the emitter. Without the dome in the way, it’s possible to make the lens retract even closer to the phosphor.
OHHH thanks man, but could you explain why? I really want to know the reasoning behind this.
If possible, can anyone explain why the dome increases lumens? doesnt the dome count as an extra medium in between the emitter and air? Sorry if I am wrong with my physics here
Cut and pasted from DrJones’ superb explanation: DrJones on flashlight optics
“What dedoming does
As written above, without the dome the photon extraction is reduced, most photons don’t get out - at the first try. But those photons aren’t lost, TIR bounces them back and gives them more chances to be diffused into a better angle and get out. That TIR back to a the diffuse LED and photon reuse is the reason why the luminance can be increased even though normal optics can’t do that. The dome actually is just some normal lens and would have no influence on luminance, but without it we get TIR and photon reuse, and those photons add to luminance.
The same trick is used with the Wavien collar: With an SST90 in an aspheric lens thrower, the light emitted to the side is lost, as it’s not caught by the lens. An additional lens as ‘pre-collimator’ may catch more flux from the LED, but that won’t give more throw, since it neither increases luminance nor the front lens area (instead the bigger caught flux is packed into a wider beam with same intensity and throw). However some clever people put a reflective collar around the lower part of the dome, so that the light that wouldn’t hit the lens anyway was back-reflected onto the die, where it additionally lights up the diffuse surface (and those photons have another chance to escape into the right direction). This effectively increases the luminance.
As a side effect, there’s a tint shift towards lower color temperatures, because the back-reflected blue photons have another chance to be converted into yellow light by the phosphor layer.
The TIR does exactly the same for the dedomed XM-L; it increases the luminance and shifts the tint towards warmer side.
Another observation can be explained by this: XM-Ls have quite some angular tint shift, i.e. the light emitted to the side is substantially more yellowish, while with the dedomed LED this effect is greatly reduced. The YAG phosphor has a refractive index of about 1.8. the critical angle agains the dome (~1.5) is about 55°, which means that such a ray to the very side has traveled a 74% longer distance through the phosphor compared to a perpendicular ray and more blue photons get converted to yellow. Without the dome, the critical angle against air is 33°, resulting in only 19% longer distance in the phosphor and thus much less angular tint shift. See these nice images by Tecmo: X-ML de-doming method with 100% success? (post #431)
Wrong/incomplete explanations
The die is smaller so the light density is higher - well, if you get about 30% less flux out of about 50% less (apparent) area with similar beam profile (lambertian), that should result in about 50% more luminance. However that’s only half of the truth: If you try to get a smaller image of the die by using a diverging lens, or by filling something around the dome to get a flat surface to cancel the magnifying effect of the dome, that would not succeed. To increase luminance the TIR light needs to be reflected back to the die, thus the reflecting surface must be very near to the die. Either you remove the dome completely or you only leave a small layer (<0.5mm).
Due to the collimating dome missing, the light from the LED has a bigger beam angle and thus more light hits the reflector - actually no. First, the beam is about lambertian (i.e. 120° FWHM angle) with or without dome (see Tecmo’s images). Second, that wouldn’t explain why aspherics get increased throw, too. And third, even if you use a more collimating dome (like XR-E), that won’t change luminance, because normal optics can’t. (The XR-E doesn’t throw so well because of the smaller beam angle, but because the EZ900 has a quite small area, thus more flux per area and thus a high luminance).
Actually the A*W rule does make the beam profile broader, broader than the hemisphere by back reflection that is. That itself doesn’t change luminance. Only if that back-reflected light hits the diffuse die again, luminance increases.”
Wow. physics. Nice find. Thanks for the link to the full post. probably going to read it 3 times for it to sink in (;
By “better” I guess you mean increased throw?
I have a Dereelight Xsearcher that has been current boosted by a bit and de-domed.
It has dramatically increased the throw and warmed up the tint by quite a bit.
Which is great ’cause I don’t like the bluish tint of the original emitter 
Dr jones talks about reflecting light back to the emitter. Anyone has some thoughts on how to do this? is aluminum foil good for this job?
The base of a Maglite reflector, turned upside down, has been used.
Use the Wavien Collar, not cheap though.