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What resistor to use on LED light?

1451 Views 11 Replies 7 Participants Last post by  DaveintheGrave
Needing a LED light for an owl that I will be lighting his eyes up with. The only LED bulbs that I can find at my Radio Shack are just the bulbs without the resistor already attached. What is the rule of thumb on this? I plan on running it with a little 9 volt battery. Is there a formula for what resistor to use for a certain sized LED light? Any advise would help greatly!
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I've built probably a hundred LED circuits consisting of two LEDs and a 9-volt battery. I always used a 330 ohm resistor with no problems.
If you had to guess, how long would that setup stay lit before the battery ran out?
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