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!
Use the link that Halstaff posted or do a search for LED calculators. Without doing any calc, a pretty safe set up is a 470 ohm 1/4 watt resistor for a single LED using up to a 12v power source.