LED resistor question...

[hairyandy]

Hey all,

A quick (hopefully) yes or no question for the peanut gallery.

Is it OK to use an 1/8th-watt resistor on an LED?  I think it is but I thought I'd put it to the board to get the definitive answer.  I recently won a lot of various resistors on Ebay and I just realized that I had a whole mess of 2k 1/8th-watt AB resistors which, coincidentally, is the value for the perfect brightness for the orange LED's that I've been using.  I'm OK using these right?

TIA

[Peter Snowberg]

Ohms law is the answer.

Print this out and hang it on your wall....



If you look in the watts section you see three formulas. Each of these can be used to find watts so we go to the one that covers the parameters we can give.

If you start with 9V and subtract the forward voltage (Vf) of the LED which is probably something like.... oh... let's say 1.6, you'll get something like 7.4 volts which is being lost over 2000 ohms. We know voltage and we know resistance so we'll use watts=volts^2/resistance, or P=E^2/R.

If we plug those numbers in we get...

Watts = (7.4^2)/2000 ...or...
Watts = 54.76/2000 ...or...
Watts = 0.02738 ...or...

27 milliwatts and a 1/8th watt resistor is good for 125 milliwatts.

In a (pea)nutshell.... Yes.

[hairyandy]

Thanks Peter!

I'm learning everyday around here.