[Sofaman]

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!

 

[Halstaff]

Here's the wizard I go by - http://led.linear1.org/led.wiz

 

[J-Man]

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.

 

[CreepyCreations]

If anyone is interested, I have a spreadsheet I put together that does all the work for you, for 1 - 5 LEDs. Just drop me a message with your email and I'll send it to you!

 

[CreepyCreations]

There's also this:

 

[Rabbit101]

Oops tried to edit my message landed up with a second message and I don't see a delete

 

[Rabbit101]

Just a thought, for an Owl instead of red or green they make FLICKER LED's in a YELLOW GOLD, so no circuit is needed just a resistor like any ordinary LED.
Only difference is they flicker!
I purchased a 100 pack for $5 or so on Ebay.

Be sure to copy the Voltages ratings of the LED's so when you use the resistor calculator you get the correct resistors for your LED's and keep a copy (I put mine in the bag of LED's)

Ebay is a great source for LED's Radio Shack has a very limited supply (great in a pinch if you need them fast)
See if the vendor has your resistors at the same time

 

[DaveintheGrave]

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.

 

[ice456789]

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?

 

[DaveintheGrave]

Well, I've never run a set continuously to see. But the battery would probably last all season, if its only run a few hours each night. The 9-volts do last a long time.

 

[CreepyCreations]

Dave, 330 ohms sounds about right for 2 LEDs on a 9 volt battery. Only about 15 mA draw, so it should last quite a while!

 

[DaveintheGrave]

Thanks, Creepy! I don't remember where I got the info. to use that resistor, but it always worked so I stuck with it all these years.