3
\$\begingroup\$

I want to put yellow leds inside the turning-signal cases used in motorcycles.

The problem is: since the case is not deep enough, when I look from far I can only see the focused, pin shaped LED sources (two, in my case).

The leds I am using are like these:

enter image description here

As I see it, the case from the motorcycle turning light is supposed to receive the an incandescent lamp, so the internal diffusions gives its whole area the same brightness as seen from far away.

So my question is: how should I "unfocus" these leds (which I already bought, by the way)?

Possible options would be:

  • Cover the led "lens" with some "cap" made of a diffusing material (semi-transparent glue?). Possible problem would be loss of effective luminous power?
  • Paint the led lens with some suitable diffusing paint or material?
  • Sand the led lens surface, so as to scatter the light?
  • Reshape the so that it distributes the light in more directions?

I know I could try every option myself, but I imagine this is not a rare situation, so perhaps someone has already done something about it.

\$\endgroup\$
  • \$\begingroup\$ A total internal reflection lens with no direct path from LED proper to you will do what you want. These are available commercially -at excessive prices ($1 +++) from western suppliers or at OK prices ($0.10 +++) for identical product from Chinese suppliers. These images and these links may help. \$\endgroup\$ – Russell McMahon Apr 12 '15 at 2:27
  • \$\begingroup\$ From far away and these. And variably far away \$\endgroup\$ – Russell McMahon Apr 12 '15 at 2:30
  • \$\begingroup\$ @RussellMcMahon What I am actually trying to do is not to focus an omnidirectional LED, but quite the opposite: to modify a led which is already focused (either by the conical metallic part inside, and also by the round lens shape of the casing itself) so that it sends light AROUND, and not almost exclusively to "the top", so to say. I added an image. \$\endgroup\$ – heltonbiker Apr 12 '15 at 2:53
  • \$\begingroup\$ (1) You can get TIR lenses that convert almost anything to anything. (2) Believe it or not (try it and you will) you can get substantially LESS directionality by simply cutting part of the top off. Probably all of the domed part and some more. Go down too far and you risk interfering with the LED proper - but you should be able to tell how much you can probably safely remove by examination. This approximates a "top hat" or "straw hat" LED. You can round the edges but this will probably not be necessary. More later maybe \$\endgroup\$ – Russell McMahon Apr 12 '15 at 5:18
3
\$\begingroup\$

A total internal reflection lens with no direct path from LED proper to subject,
or a Fresnel lens based "diffuser" will do what you want.

These are available commercially at from about $0.50 from western suppliers and for much less for identical product from Chinese suppliers. See below.

TIR or Fresnel lenses are available which will convert almost anything to anything - including light from narrow angle through hole LEDs to very wide angle radiation.


Cheaper, easier, maybe good enough:

Wide angle through hole LEDs are often referred to as Top Hat or Straw Hat LEDs due to their shape. The die is close to the external face and the package is often blunt ended to obtain the required radiation tpattern.

You can get substantially LESS directionality from a typical existing epoxy encapsulated through hole mount LED by simply cutting part of the top off so that the end is "squarish" and closer to the die. In this case, cut off probably all of the domed part and some more. Go down too far and you risk interfering with the LED proper - but you should be able to tell how much you can probably safely remove by examination. This approximates a "top hat" or "straw hat" LED. You can round the edges but this will probably not be necessary. Practice on a cheap LED first :-).

Commercial "straw hat" wide-angle LED.

enter image description here


Wide angle domed orange Fresnel add on lens for 5mm through hole LED.

Data sheet - brief

Pricing - in stock in 1's $1.04

enter image description here

In stock Digikey in 1's


Squarer Fresnel for 5mm surface mount LED

enter image description here

Dimensions

Data sheet - poor

\$\endgroup\$
  • \$\begingroup\$ Thanks very much for your help! Since the leds I'm getting from my local store are limited to round top (at least for amber/yellow color), and are quite cheap, I'll try adding the "M&M sized aluminum foil" mentioned in the other answer, since it seems easy enough and makes a lot of sense. I have already sawed off the top of one of the leds and the results were mixed: it diffuses a lot more, but still looking through the amber plastic (which is too close to the led, when everything is mounted), I can still see a small light dot. So the two-step reflection is something to be tried. \$\endgroup\$ – heltonbiker Apr 12 '15 at 14:19
2
\$\begingroup\$

You should try sanding. Rub a fine sandpaper (such as 400 grit) all over the lens of the LED until it looks opaque or covered in white dust.

\$\endgroup\$
2
\$\begingroup\$

The way larger encasements do it is by using a small conical mirror right in front of the bulb to reflect almost all of the light back on to the larger concave mirror. (Example)

We can use this same idea in a smaller way: use a small M&M-sized piece of aluminum foil placed directly in front of LED (glued to inside of translucent cover) to reflect focused light back to the source, and more foil around the led to spread out the light.

As long as you can open up the encasement, it should work regardless of the size.

\$\endgroup\$
  • \$\begingroup\$ Good idea, gonna try it as soon as I get the time for it! Thanks for now! \$\endgroup\$ – heltonbiker Apr 12 '15 at 1:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.