I need help setting up an LED experiment for class

For my physics class, I was told to design an experiment involving ANYTHING. So I chose LEDs and optics. Since Lux Is are expensive, can I run 5mms behind various optics? (SO17, Fraen LP, etc)

This trick takes a bit of work, but it works. Get a stiff emery board. Dollar stores useually have them, mine is about 1" x 6". File the LED flat until just above where the bond wire is, then round it off to get a slight dome. Then use the finest sanding paper you can find. I use 1200grit, and smooth it as best you can. then do a final polish sanding with a bill of US currency, The NEW 20's work best, but any bill not super worn works well. This will give you a light source with close to a 180 degree output. I have used this method, and it works with reflectors as well as LUX optics.

Hope this helps

Jeff

Ok, what can I do with them? I need an idea on "what's the point of my project?" Should I try to maximize lux?

Re: I need help setting up an LED experiment for c

Big reflectors versus small ones.
Shallow versus deep.
These kinds of things may work.

There a physics in the way different reflectors work.

A 5mm led throwing a spot onto the ceiling in a mag reflector may well impress the class.

Re: I need help setting up an LED experiment for c

Where can I get cheap optics/reflectors?

Re: I need help setting up an LED experiment for c

Color mixing? Comparative efficiency of different lighting types? The nature or behavior of light? The nature of color perception?

Re: I need help setting up an LED experiment for c

Yard sales, second hand stores, dollar stores, even here on cpf in the bst lights forum.

WTB assorted optics and reflectors new or used.

Something like that perhaps.

Re: I need help setting up an LED experiment for c

Maybe you can combine different colors of LEDs with a silicon photocell to show the differences in sensitivity of the cell at different wavelengths? Maybe compare it with a selenium photocell?

Or aim a white LED at a diffraction grating or a prism to separate the colors and show the spectral content; then shine an RGB LED through the same optics to demonstrate that while both experiments produce "white" light, the different sources have significantly different spectral content. The point of the experiment could be to show that our perception of white light can be subjective.

Another thought - show a spectrum of LEDs from red through UV, then show how the blue and UV LEDs can cure a patch of epoxy. Then explain the progressively higher energy contained in the shorter wavelengths.

Good luck with whatever you choose!

Re: I need help setting up an LED experiment for c

Or try demonstrating:

1) The current output of a solar cell using different color/powered LEDs. ( in conjunction with diffraction grating or prism analysis pointed out by PhotoWrangler)

2) Irradiate/Charging glow powder with different photon sources ( laser, LEDs, UV.. ) and explain the interaction with photons and electrons and the energy bands/decays..

3) Photon transmission test using various lens material and coating. Some materials are opaque in visible spectrum, while total transparent in UV range.

4) Optical Fourier Transform using laser.. fun!! but very involved.

Read "Lectures on Physics" by Richard Feynman

Re: I need help setting up an LED experiment for c

i've done this experiment. it's neat to shoot sound across a room with a beam of light.

uses really basic circuitry and a photocell connected to an amp/speaker. easy to do also.

http://home.earthlink.net/~lenyr/modlitbm.htm

you can also do something with the Total Internal Reflection principal. and bring in a surefire or an Inova X or T series and blind people.

Re: I need help setting up an LED experiment for c

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i've done this experiment. it's neat to shoot sound across a room with a beam of light.


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Sounds like something that I had wanted to try as a variation on a published circuit, but never got around to photocopying the article before the magazine "walked" out of the school library. It was a class "D" amplifier (high-frequency square wave with its duty cycle modulated by the audio signal). My theory was that if the output were fed to an LED instead of a speaker, a photocell/amplifier circuit like yours would be usable as a receiver.

This was back in the early '80s, when Radio Shack sold a plastic 5-cell flashlight with a (roughly) 4" reflector - it made a stock Mag look good, but it was cheap. This would have been a good housing for such a project - comes complete with battery housing and switch, and the "business end" is big enough for a circuit board (including audio input jack and the LED).

Re: I need help setting up an LED experiment for c

Neat ideas above; I like the photocell-audio-amp experiment. I've done this myself and it's great fun "listening" to modulated light from unexpected sources.

Speaking of, how about a laser-bounce listening system? You can use any old laser pointer along with a photovoltaic cell (not a CdS cell!), a receiving optic and an audio amp. Bounce the beam off a window and focus the reflection onto the photocell to hear whatever the window hears as it's modulated by the sound waves striking it. Kind of a "dark" project but still interesting.

Re: I need help setting up an LED experiment for c

Thanks