Date:         Fri, 26 Jul 1996 23:45:52 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         natasha!kombi@adobe.mv.us.adobe.com
Subject:      Re: basic electronics question

> Okay, now that there have been at least 6 different answers to what
> resistor to use for the LED.  Who has the final answer?  This has been an
> interesting string!!
> 
> James

The higher values are the safer ones, they pass less current, and generate
less heat.  I think all six answers were in the 200-300 ohm range, so there
are not wildly differing views.  I suspect all responders would not care if
the 300 ohm value was the chosen one -- you just won't get as much light out.
If you use the low end, you risk burning out your diode.  Since a 1-watt 
(or even the 1/2 watt -- I think all were agreed on that) resistor is likely
to be a 20% tolerance part, a 250 ohm resistor (meaning it's somewhere
between 200 and 300 ohms) covers all of the responses.

At 200 ohms, 60ma will be passed, which is *probably* ok, at 300 ohms only
40ma will be passed, which will not provide full brightness.  Either of
these extremes is probably acceptable.  If they're not, you will have to
find a more accurate resistor, or select one with an ohmmeter from a batch.
Anything in this range is also probably ok -- it is certainly safe in the
upper half of the range, so all of us pretty much gave the same answer...

malcolm