How to reduce light loss in a zoomie torch when zoomed in

[EasyB]

@scianiac

To put some numbers in I compared an XP-L’s spatial distribution curve against the “acceptance” angle of a C8 reflector and a Z1 lens. Being 28.9 and 37.2 respectively. The C8 gets all the area under the curve after 28.9 degrees and the Z1 gets all the area before 37.2 degrees. Of course I’m just counting squares here so not exactly precision science but they are 7.5 and 10 respectively. So the Z1 lens is able to put more lumens (which are cd*sr after all, the chart being cd percentage and angle) into it’s beam than the C8 into it’s hotspot. This thread may be getting a bit more complicated than the OP intended….

This is an incorrect conclusion. The emission pattern on the XPL datasheet tells you the intensity at different angles, but it doesn’t tell you the total amount of light at different angles. To get the total amount of light you have to integrate around the axis perpendicular to the LED surface. The resulting pattern looks like the picture in this post:

[PART 1] Official BLF GT Group Buy thread. Group buy officially closed! Lights shipping.

That’s cool, would you mind sharing that function? How did you interpolate the curve? I took the closest possible parabola to it, there is no easy way to make a function that copies the intensity curve unless you use piecewise, which I might try to do, or might not Anyway, it is pretty accurate. 0 to 100% intensity, –90 to +90 degrees. [image] Orange is the function, white is the intensity curve from cree. Function is y=-.015x^2+100\left\y>0\right\ Green line at y=–1 …

A bit more explanation here:

BLF recoil über-thrower

I’m not trying to dissuade anyone from building a recoil reflector light, but it seems some are overestimating the improvement in light collection efficiency of a recoil setup over a traditional reflector setup. A typical traditional reflector (like a C8 reflector) already collects 75% of the light emitted (lumens) from the LED, so collecting 100% of the light would only be a 33% improvement. If you are trying to think about the total light collected by a reflector, the intensity vs angle plot…

The thread I posted above in post #4 also has some discussion of the light collection efficiency of a lens light and how a precollimator lens can improve it.

It turns out the C8 reflector collects ~75% of the light into the beam. Aspheric lens lights tend to have much worse efficiency ~25%. This is supported by measurements that djozz did.