Ideas for a diffuser for an LED

Martin_H

I have a blue super bright LED which I've been using with my line scan camera. The light spot it produces is too focused and unevenly illuminates the subject. So I made a diffuser out of tissue which improved things, but there's still a bright spot from uneven illumination. Some scheme to better diffuse the light is in order, but I am not sure what.

Any ideas for a fool proof diffuser? Either that or I build a different LED using several wide angle LED's in a row.

Phil Pilgrim (PhiPi)

Martin,

Unless you're doing RGB color vision, you're not doing yourself any favors by using blue, since that's the color the TSL1401 is least sensitive to. I would suggest red instead.

I would also suggest using so-called "superflux" LEDs in a P4 (aka "Piranha") housing. These typically have a very wide-agnle spread and even light distribution, which is ideal for the TSL1401-DB.

If you feel you must use a diffuser, request samples of holographic diffusers from these guys:

http://www.luminitco.com/

They will give you the most even illumination possible.

-Phil

HollyMinkowski

I know that if an LED has a flat top the light spreads out in a huge angle.
Perhaps you can somehow grind the top of your LED flat?

I bought a 100 pak of super bright, white, flat-top LEDs on ebay for 5 USD
and the light spreads out almost like it is from a point source.

Martin_H

Thanks Phil, I'll take a look at the other LED's you mentioned. I happened to have this insanely bright LED on hand, but I'm not wedded to using it.

Martin_H

If I go for immediate gratification. It looks like Radio Shack carries a red wide angle LED in the P4 housing.

http://www.radioshack.com/product/index.jsp?productId=3097459&filterName=Type&filterValue=Specialty#

Phil Pilgrim (PhiPi)

Thanks, Martin! I didn't know RS carried those, and the local shop shows them in stock. I'm going to go down there right now and get one to check it out.

-Phil

skylight

@ Martin_H I use filter gels/paper for work and could post you some diffusion, PM me and i'll send you some cutoffs.

Phil Pilgrim (PhiPi)

Just tried the RS LED. With a 5V supply and a 47-ohm series resistor, it draws about 46 mA. It's very bright and provides even illumination over a wide angle.

-Phil

Mark_T

Another way to diffuse is to sand the LED package with thoroughly with coarse sandpaper - instance ground-glass-like diffuser!

Martin_H

I went to two local Radio Shacks and both had the green, white, and blue colors of the piranha LED, but no red. So I decided to take a chance on green as likely being a better second choice than blue or white. I should be able to wire this up tonight and see how it works.

I also searched with Google and apparently grinding the top of an LED flat is a common way to get a more defuse output. I might try that at some point with the existing LED.

Duane Degn

I'd suggest a combination of Holly's and Mark's ideas.

Sand the dome off the LED and leave the flat suface rough.

Edit: Martin, I hadn't seen you last post. I think the first time I read about sanding the dome off a LED was in an article by JonnyMac in Nuts & Volts.

Martin_H

I tried the piranha LED and it works quite well. Below is a screen capture of the raw unprocessed output from the TSL1401 monitor showing the brightness across the field of view. At the top is an image of a pure white background resulting in a fairly straight line, while an image of a black line against a white background yields a noticeable depression where the line is located. With the old LED the image was significantly brighter towards the center which could mask the presence of a line.

Here's the new LED lamp plugged into the TSL1401.

I use a 2N2222 to provide current to the LED since the Propeller doesn't have the current output for this sort of LED.

Sariel

I know I am a bit late to the party, but a few years ago, I had the same question come when production wanted a "Light Bright" kind of setup for putting dummy terminals in d-sub connectors. All they wanted to have was a mate connector that they plug into, and can see pins of light come through where they need to put in a dummy pin. All I had to do was build the housing, take a mate connector, drill some of the holes a bit bigger, then fill the "Blocked" ones with epoxy.

Top cutaway view
     Face of D-Sub mate connector
       ┌──────────────┐
      ┌┴──────────────┴┐
      │                │
┌─────┴────────────────┴─────┐
│                    ─── Stand offs
│   ────────────────────── ─── White Copy Paper (Sheet or two, depending on the brightness you want)
│         LED's        │
│     ‣‣‣‣‣‣‣‣‣‣‣‣     │  
│     ‣‣‣‣‣‣‣‣‣‣‣‣     │                    
│     ─── PCB
│                      │ 
│                      │ 
└────────────────────────────┘

It ended up working quite well, and I have made a couple of these using super high brightness Blue LED's with standard dome top. Just put in a row of the LED's and the paper does the rest.

MUCH easier and cheaper than the "Fiber Optic" idea my boss had !!