Hi, my first post.
I applaud and am appalled in equal measure you guys!
I looked on the web for information before doing a torch mod.
I found you guys and I’m impressed with your skill and enthusiasm.
I do optics as part of work and as a hobby.
I have an old Screwfix 55w 6v halogen hand grip spotlight which was used in timelapse night photography shots. The SLA battery has died, so I am making it a donor for an LED spotlight.
So with a Cree XPG on hand from the junk box, I look up the best way to do this.
What about the mirror from the old light? Not very good with an LED, see the link below.
What about the two plastic parabolic mirrors from a Tobar Mirascope optical toy? I found one in the junk box too.
So I’ve made a radial heatsink with 18 thin copper fins and a rear-facing LED. Throw looks good. Nice image of LED die on the clouds.
Shame about having to link photos from Dropbox or URL. I took some build photos as I went along.
There’s lot’s of really great stuff on this forum, so thanks for the chance to see some of it.
Looking up LEDs and mirror collimating I found this reference;the light cone that misses a parabolic mirror is collimated by a seperate small aspheric with the same focal length mounted in front of the LED -
page 302 Optics for LED Packages and Applications - Kai Wang, Sheng Liu, Xiaobing Luo, Dan Wu - Google Books
The single optic truncated parabolic mirror design is adopted in commercial hand torches.A lot of the emitted LED lumens just spill out onto the general direction in which it is pointed, like a flood light. It just seems strange to me, a wider beam if wanted can be obtained just by a little defocus once the optic has collimated all the light. Which a simple rear facing arrangement can do very well.
Once you can find a source for the parabolic mirrors of a useful focal length, like 45mm, which is what my Mirascope ones were and 120mm diameter.
I am tempted to swap the XPG for an XHP35 HI and see if it really does have the same illuminated die dimensions but without a dome and 3 times the lumens.
Cheers,
Grumpy Mark