What resistor for an unknown LED?

**limpet** · 9th July 2013, 15:08

I want to run an led on 18v for power indication but I don't know the led specs.
Can anyone give me a rough idea of the resistance needed?
Thanks

**PJ-27** · 9th July 2013, 15:52

I use this tool:

http://led.linear1.org/1led.wiz

It has info on what stats common colours carry.

**limpet** · 12th July 2013, 22:32

Thanks, I put some average specs in and it said 820ohm, so I've got 4x 200ohm that I had lying around and it seems to be ok.

**PJ-27** · 13th July 2013, 10:09

Sounds about right.

**typhoon_driver** · 13th July 2013, 12:05

Could always just measure the led resistance with a multimeter

**limpet** · 18th July 2013, 09:17

Originally Posted by typhoon_driver

Could always just measure the led resistance with a multimeter

I can do that easy enough and it would make it easier for unknown LEDs, how can I work out the required resistor from that though is there a formula?

Thread: What resistor for an unknown LED?