LED resistor value

[CCS]

Hi All - what resistor value should I use with 9 volt power source to run a single LED in a pedal.
Is there a one size fits all for any colour LED? Cheers Paul

[BrianS]

I use an 1.8k or 2.2k most of the time. 

[Jules]

2.2k and 4.7k are pretty common with a diffused Led.
Can be be up to 22k for the clear bright type.
No hard rules though.

[WormBoy]

If you know or can find the properties of the LED (forward voltage and current) you can use one of the online calculators. When in doubt, use some alligator clips, hook up the LED to 9v, and try different resistors. As Jules already said: the clear LEDs might need a big resistor otherwise you will have a lighthouse on your pedalboard.

[somnif]

Oh yeah, I remember this. My first pedal had a 4.7k LDR on the schematic, and I didn't think about it when filling the slot. I then used a waterclear ultrabright blue LED on the thing.

Damn pedal practically works as a room light.

I now use a 50k linear pot to test LEDs. Hook up a 9v battery, attach the pot to the LED, LED to battery, and twist the pot until you achieve your desired brightness. Then test the resistance across the lugs of the pot. (for added safety one could conceivably add a ~1k res in series with the pot just to make sure you never accidentally zero it out and cook your LED, but I'm lazy)

Turns out the Blues I had at the time were still fairly bright with a 47k LDR on them. Waterclear whites I end up around 27-33k, and so on down the line. Only really need to test each batch once, but every time I get a new brand or new color I pull the old rig out. Haven't found anything that needed bigger than 50k on them

[alanp]

The lower the resistor value, the more current flows through the LED (causing more light.)

Different LED models have different efficiencies. 20mA for one LED might be equivalent brightness to 2mA on another LED.

[Aleph Null]

Brightness will vary. I've found I can reliably get satisfactory results using cheap diffused LEDs and 4.7k resistors. There is some variation from color to color, but nothing drastic. As others have said, super-brights and water-clears are different animals.

[CCS]

Thanks for all responses