Monday, February 2, 2009

Mucking Around with LEDs, Acrylic, Diffusers

Seems that there are many things to fiddle around with regarding the LEDs, and how the light shines through the perspex...

I did a few experiments to see what the overall effect was.

Using Aluminum Foil Sandwiches

I figured that by placing aluminum foil at strategic places between the layers of perspex I would be able to control how much light was radiated forward out the face of the plastic, compared to how much was reflected out from the back side...

So - I set up the following configuration of an LED with some layers of perspex.



The setup had one face plate of perspex, with two back layers with holes through them. The LED poked through the two perspex layers from the back. The whole thing was held together with a plastic clamp. The LED was driven by around 3 volts via two 1.5 V batteries in series.

Test #1 was without any aluminum in the setup... with the light pattern as follows



(I laid a ruler on top to get an idea of the size of the light patch that appeared).

Test #2 added a layer of aluminum foil behind the face plate of perspex, with a hole in the center corresponding to the hole in the other perspex sheets.



With the resulting light patch as follows



Difficult to tell what the difference is.... maybe the colour is different - but that is likely to be from the camera exposure differences... the size of the light patch is very similar.

Test #3, moving the aluminum foil back one layer...



Gives the following light pattern



Again - not much difference - similar size of light patch...

Test #4, final version was with the aluminum all the way covering the back of the setup...



With the resulting light pattern



Maybe with this one, there is a slight increase in the size of the light patch - but maybe not. Difficult to tell with these results.
My gut feel is that with the aluminum closer towards the front - it cuts down a little on the light traveling towards the front plate. As you move the aluminum back in layers, the amount of light going forward increases, with also some boost from the reflected light via the aluminum - however the reflected light has to travel through lots of plastic to reach the front.

So - you can see that I have no idea how useful it is to layer aluminum around the perspex bits :-)

Using Diffusers (Actually - is just a reflector)


A quick bit of Googling and YouTubing gave me some more inspiration. I cam up with the following test configuration to test how using diffusers I could get a more even light distribution as seen from the perspex face plate.



The setup has the LED at the bottom, shining onto the back of the face plate. I then simply view the light pattern on this plastic sheet from the top.
With this base configuration, the following pattern appears.



This has a clear central bright patch, with some rings as you move outwards - not really an even spread of light.

Diffuser #1 was a simple cone piece of paper



Which when fitted looks like this



and gives the following light pattern



Now, I think I can see a clear difference from the image without any diffuser. The image now seems to be a little more consistent in terms of illumination - there are still the rings visible, and bright center - but better consistency. The overall distant spread of light is also reduced.

Diffuser #2 - I added some aluminum foil lining into the paper cone.



Which gave the following pattern



I think it is an incremental improvement from the paper only diffuser. The contrast between the bright center patch and the rest of the light patch is reduced a little - maybe :-).


So What Does It All Mean ??

I think it means that maybe there is a way of getting a more consistent, even spread of LED light for the power button. However it would mean doing some design changes for how things are put together... and probably produce a more chunky switch.
I have no idea how to incorporate the diffuser idea into the switch... requires some more thinking I suppose...

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