In the last week no fewer than two people (yes two! More if you include Linear's mockings) have accused me of being an 'LED' guru - so I thought it was probably about time I set the record straight by republishing this guide.
Please don't try this at home, and if you're looking for a good definition of the word stupidity try 'Cheese, the chap who accidentally blew up an LED the day after writing this guide'. On with the show,
I was playing with some new LED's recently when I found out how easy they are to destroy. I mounted a 4V yellow 5mm LED in a holder and slowly increased the voltage across the LED to 5V - at only 1V above its rated maximum it stopped working and started burning after about 10 seconds (I should probably warn you that the smoke produced by the burning LED here was probably toxic, so don't try this at home). It's clearly very important that you don't overload your LED's and if you're using a supply voltage higher than the LED's recommended forward voltage then wire the LED in series with a sufficiently large resistor (this page very helpfully calculates the resistor value you'll need - cheers linear).
This said the burning was quite impressive and I had lots of spare LED's so I decided to try again and this time take some pictures, err... so you guys would know what to look out for and avoid (of course!).
Not quite satisfied with a few pictures I thought I'd repeat the experiment with my camera (still working!) in movie mode. Sadly it only burnt this time (and there wasn't even smoke!) but have a look at the movie anyway (it's only 100k and has a good soundtrack!) - here.
Well I think I've learnt my lesson now and shown you why using the correct resistor with your LED's is very important.