Led Resistor chart

[clamup1]

hey i was digging through the archives and found a post where someone layed out the color led and the resistors value to use. i cant find this post has anyone seen it or happen to save it

[petemoore]

  try AMZ labs notebook 'online calculators'?

[darron]

The colour alone isn't really a good indication of how bright the LED will be, or how much current to limit. They all vary. Especially, of course, the new style clear ones where you'd need to look at the datasheet, or otherwise just use trial and error.

[R.G.]

There is a **great** way to do this that doesn't need finding old posts or online calculators.

1. Get a battery and a 4.7K resistor, a multimeter and the LED you want to use.

2. Oh, wait. If you haven't ordered the LED yet, **look in the catalog you order from or the manufacturer's datasheet ** and they'll just tell you the LED voltage. This is what you're looking for, as it happens. Everything else flows out of that.

3. Back on track. Hook the battery, resistor and LED in a nice, circular ring. If the LED does not glow, it's backwards. Reverse it until it give out light.

4. Measure the voltage across the LED. It will be between 1.2V and 5Vdc. Write that down. As an example, imagine you measure 2.1V.

5. Now the hard part - gotta use a calculator and do ... subtraction and long division! If you're going to use the LED on a 9V source, subtract the LED voltage you wrote down from 9V. This is the voltage that will appear across the resistor you use.

6. How bright do you want it to be? Yep, that's a hard question. Let me make it easier. You can use any current in the LED from microamps up to 20ma. 20ma is the maximum current most LEDs in the standard "T 1 3/4" package can use without burning up. Let's say you want it bright, and make it 20ma.

7. Divide the voltage from (5) by 0.020 (that is, 20ma, or 20 1/1000th of an ampere). For our example of 2.1V, the calculation is 2.1V/0.020A = 105 ohms. This is the **smallest** resistor you can use for that LED without burning it out. Using any bigger resistor, like 240 ohms, 1K, or 3.3K will make less current flow, and make the LED dimmer. =>You can set it to whatever brightness YOU want. <=

8. Like a different LED? Just get out your multimeter and calculator. All done.

[CynicalMan]

My personal rule of thumb: 4.7k for clear LEDs, 1k for diffused LEDs at 9V. Test those out on a breadboard and tweak them to your preference. Calculating is useful, but I find it easier to just breadboard, as I can't mentally translate current to brightness.

[clamup1]

thanks for the help guys. i prob shouldnt even get into putting leds into my pedals with the probs im having right now. but i put one into my fuzz face and it worked.

R.G.- ill write that down and tape it to the wall so i dont loose it

the chart i was looking for listed all the resistor values for the different color leds. it might have been on another forum i dont remember. but i dont need it now :p

thanks again

[LucifersTrip]

the chart i was looking for listed all the resistor values for the different color leds. it might have been on another forum i dont remember. but i dont need it now :p

right, plus it's kind of useless. what's the chance the guy who made the chart wants the same brightness as you.
If the chart had the minimum ohm resistor that you need for each specific color, that'd be usefull

...just put a 5K pot in series with one lug of the led and turn it to the desired brightness, then measure the pot.
don't turn it to zero!

good luck

[deadastronaut]

funny i just got a load of leds different colours and went through them with resistors....heres my anti - blinding but still bright enough list...

all clear lenses by the way..moderate to retina destroying order.

green 4.7k..    2.2k
blue 1k           470r
yellow 470r     220r
orange 470r    220r
red 1k...         470

this was to get them to similar brightness...

[digi2t]

Hmmm.... I'm almost tempted to start using a 10K multi-turn trimmer on the board just for the LED's now.

A sort of "set and forget" dimmer... of sorts 

Cheers,
Dino

[R.G.]

Hmmm.... I'm almost tempted to start using a 10K multi-turn trimmer on the board just for the LED's now.

A sort of "set and forget" dimmer... of sorts 

Not a bad idea - but if you ever turn it all the way down you can damage either the LED or pot with the high currents when the pot goes to zero resistance or almost zero. Better to put some minimum resistor in series with it. Better yet, use an NPN as a current source and use the pot to set the current in the resistor.

[digi2t]

Thanks R.G., I hadn't thought about that. Excellent suggestion on the NPN as well. In the end I was just being a smart-ass about the dimmer. I don't think I could ever see myself going there, wasting a trimmer for that and all. In the end, I believe the K.I.S.S. principle should apply; Keep It Simple Stupid. Besides, a resistor is cheaper (and smaller) than a trimmer.

That's why I love this forum. Every time I come here, I seem to go to bed a bit less stupid at night.

Cheers,
Dino