modifying a LED

[david_winstanley]

Im in process of making a rear bike light and ive sourced some real high power red leds ( 10+ MCD) but they are very narrow angle . is there a way i can make them wide angle . ive seen some leds that seem to have been attacked with sandpaper - would presume that this acts as a defractor (of a kind) but ive also seen some that appear to have been sliced in half ??? does removing the dome make them wideangle ??????

any help would be appreciated as i dont want to be run over /ubbthreads/images/graemlins/help.gif

/ubbthreads/images/graemlins/blush.gif

 

[Lynx_Arc]

if you are talking about 5mm LEDs there was a thread on premade rear bike lights with 5 red LEDs in them and with flashing patterns also programmed into a chip. If you are going to make one I recommend just using several LEDs at differing angles or buying a premade one.
Most likely anything you do to reduce the angle is going to reduce the output of the LED with exception of some sort of optic.

 

[Steelwolf]

I've been fairly successful at modifying my 20deg LEDs to have absolutely no focus (I was building a booklight). There does not appear to be any reduction in total light output.

The basic idea is to get rid of the dome (watch out that you don't cut too deep and damage the wires going in to the die). I did this with a Dremel Cutoff wheel. Make sure you leave some material behind so that you can polish it. Apply very light pressure during polishing and rinse thoroughly between steps.

I started with 1600 grit wet/dry sandpaper, used wet, to remove any deep scratches. Done properly, the cutoff wheel doesn't leave any deep gouges, so 1600 grit as a starting point is fine.

This is followed by jeweller's rouge. It is a very fine polishing compound. You can also use stuff like Cut & Polish compounds available from the car care department, or basically anything with the equivalent of at least 3200 grit. This is usually enough, but I'm told that it is possible to obtain 6400 grit alumina or diamond powder, suspended in liquid. This should give you a finish as clear as crystal. I have even used toothpaste and gotten quite a good result. Note that it must be the white paste, not the gels.

The whole process is usually quite fast with a Dremel, but you do have to watch out not to overheat the plastic.

 

[kenny]

The very high output red LED's that I have seen are really unacceptable for what you are doing. If you go to a 15 or 20 degree LED you don't really drop that much in intensity, but you get a better spread. I replaced all of mine that I got in a ready-made Vista light with ones from Superbrightleds.com I'm a reall do-it-yourselfer, but this one isn't worth it. With the store-bought one you get the board, the leds the housing (which is virtually water-ptoof), the the mounting hardware for your bike -- all for around $14 bucks from Performance bikes or Nashbar, Supergo etc. If you have a real hankering, like I did, you can swap out the lights for some slightly better ones, though only marginally so.

As for the angle, most trafic [that you can't see] approaches from the rear and 15-20 degress is plenty for them to see. from the side, as when crossing the road -- best that you see them and wear some reflective coating. Most LED rear bike lights don't have too much spill to the side. If that bugs you, you could jack one of the LED's to the side for more coverage, but I wouldn't sand the surface or spead the light too wide or you lose intensity -- which thing you need. The Vista light I got was the more expensive of the units they sell and has around 10 or so LED's -- you can see it from WAY back.