LED viewing angles?

[signalman72]

I have a project where I need to illuminate a white plastic lens with a light from behind. Incandescent bulbs do a good job of this, but draw too much current for my application. I've tried using regular LEDs to accomplish this task, but they create an undesirable pinpoint of light on the lens. I'm looking for uniform brightness across the lens. I have no experience with wide angle LEDs. Would they accomplish the task?

 

[Harald Kapp]

Do you mean a single LED or an LED lamp?

A single LED is more or less a point source with a directional characteristic. The case can incorporate a lens to bundle or to spread the light. To distribute the light from the LED proper through the case I have in the past sucessfully used sandpaper to roughen the case of a clear 5mm LED so it becomes milky. This distributes the light from the chip surprisingly well into all directions.

 

[signalman72]

Single LED. I have found flat top LEDs for sale online that claim to have a 120° viewing angle (which would work just fine for my needs) but I am wondering if the light is nicely diffused over that radius or if there is still some focal point in it.

Thanks!

 

[Arouse1973]

You can get some very wide angle LEDs now the widest I have seen is 150deg. Try some wider versions and also move the LED further away if possible. If you can't do that then have a look at LED collimators.
Adam

 

[Arouse1973]

Do you mean a single LED or an LED lamp?

A single LED is more or less a point source with a directional characteristic. The case can incorporate a lens to bundle or to spread the light. To distribute the light from the LED proper through the case I have in the past sucessfully used sandpaper to roughen the case of a clear 5mm LED so it becomes milky. This distributes the light from the chip surprisingly well into all directions.

Good Idea Harald

 

[signalman72]

Harald, what kind of sandpaper? I've got some fine emery cloth, will that suffice?

 

[Harald Kapp]

There will probably be an uneven distribution with a focus in the center of the LED, I confess I haven't tried this before. Give it a try, you can always frost the lens later.

 

[Harald Kapp]

The grain size of the sandpaper (emery cloth) is not really important. It may take a few seconds longer or not to frost the lens using fine grained or coarse grained paper. You can even use a file or any tool that disrupts the normally clear and even surface of the LED's lens.

 

[signalman72]

Thanks again!

BTW, what's the theory behind the "frosting"? Is it like creating little micro-mirrors that scatter the light in all different directions?

 

[kpatz]

Thanks again!

BTW, what's the theory behind the "frosting"? Is it like creating little micro-mirrors that scatter the light in all different directions?

It diffuses the light, sending it off in different directions. It's similar in premise to the frosted coating on the inside of a light bulb, gives a more uniform light than a clear light bulb.