LED limiting resistor values

[dumbmonkey]

Hi,
I have a question about the limiting resistor for LEDs.  I'm a total neophyte here, so please bear with me.  I've completed a couple of builds (Red LLama, and Green Ringer) and have used blue 5mm LEDs for Pedal Parts Plus (great people, by the way).  I used 4.7k as the limiting resistors, and the LED is bright.  Really bright.  I think I need to move to a higher value resistor.  I realize that there are calculators that I can use to figure out values, but as I said, I'm totally new to this, so the technical aspect is pretty confusing to me.  Can anyone recommend values that I might try? Should I just hook an LED up to a battery and try different size resistors to see what works best? 
Thanks in advance,
Chris

[CGDARK]

Hi,
I have a question about the limiting resistor for LEDs.  I'm a total neophyte here, so please bear with me.  I've completed a couple of builds (Red LLama, and Green Ringer) and have used blue 5mm LEDs for Pedal Parts Plus (great people, by the way).  I used 4.7k as the limiting resistors, and the LED is bright.  Really bright.  I think I need to move to a higher value resistor.  I realize that there are calculators that I can use to figure out values, but as I said, I'm totally new to this, so the technical aspect is pretty confusing to me.  Can anyone recommend values that I might try? Should I just hook an LED up to a battery and try different size resistors to see what works best? 
Thanks in advance,
Chris

Yes, blue LEDs are really bright but you can raise the resistor value to 10k or even higher depending of how bright you want the LED.

Here's a good current limiting resistor calculator:

http://www.muzique.com/schem/led.htm

Good luck,

CG

[R.G.]

In this case, using the special purpose calculator will keep you from learning what's going on.

Which is a shame, because you have a good handle on the operation intuitively. What you're missing is that LEDs have a light output proportional to the current that flows in them, and possibly that for a given voltage, doubling the resistance halves the current. Later  you'll learn V=I*R as Ohm's law.

So if it's too bright, you can about half the brightness by doubling the resistor. Got 4.7K now? Put in 10K, a little more than double. Still too bight? put in 20K or 22K.

There are some nonlinear things you run into, but this is a beautifully linear one.

Skip the special calculators - you'll have a much better feel for what a circuit does.

[Dragonfly]

On ultrabrights I typically use a 15k resistor. The LED is still bright, but the current draw is lower.

[dumbmonkey]

Thanks everyone.  I really appreciate the help.  I figured that adding resistance would do the trick, I just wanted to run it up the flagpole.  You all have always been very helpful and your insights are well taken.
Chris

[blanik]

a good trick is also to put a 50k pot between the + and the LED, adjust it to taste then check resistance with you DMM, it will give you the value you need...

(tip: if you plan on using your pedal mainly with batteries, adjust the LED so you can see it but not too brightly, it will result in a higher value, thus stretching your battery life)

[BubbaKahuna]

Before you tweak your LED to perfect brightness on your bench, try it in full sunlight.
What works great in a normaly lit room 1 foot from your face is often completely useless under the sun 6+ feet away from your eyes.
Nothing more frustrating than looking down between songs at an outdoor gig and having no clue what's on or off until you make noise. 

Personally, I love the super bright blue LEDs. No guesswork - that's for sure.

If I ever (rarely) mess with different LED limiting resistors, I use a 100k linear pot, twist to taste and measure resistance.

[Myriad Society]

I do pretty much the same thing that BubbaKahuna does when deciding what value my LED resistor(s) is going to be. You also have to factor in the opposite side of the coin too though. While it is important that you can see whether or not your effect is on or off in full sunlight you should also factor in the brightness of it when you are in relatively dark conditions such as the dark stage of a bar or night club you (or someone who is using your pedal) may be performing at.

If the LED is too bright, the light emitted from it can flare on the lenses of your eyes (just like a camera) when viewed from an overhead angle making it extremely difficult to tweak pedal settings in the dark quickly between songs when needed. This may not be too big of a problem in and of itself but can easily be compounded if you take into account that those of us who build effects tend to like using our own builds in our rigs. In that scenario it's quite likely that any one of us could end up with 5 or 6 pedals in a row, all in the exact same size enclosure and all with bright blue LEDs which could potentially be difficult to tell apart from one another on a dark stage whith a whole bunch of overly bright LEDs obscuring your vision.

I guess I'm just trying to say that you should eyeball test your brightness under both extremes and try to find the happy medium. Current draw for one LED in most pedals is typically a non-issue but should still be considered nonetheless and by finding a good medium brightness to the eye, you will also be finding a good medium current draw by default. As R.G. just brought up: "...LEDs have a light output proportional to the current that flows in them...".

One last thing that I like about BubbaKahuna's method is that it makes for a very quick and easy way of matching the brightness of LEDs when you have more than one in a single pedal. Generally speaking, when you use multiple LEDs in a pedal they are as indicators for different switchable aspects of the effect - typically whether something is on or off. So you may have a blue LED for the standard "bypass indicator" and if it were an overdrive you could install a red LED on a footswitch that that lifts an extra diode from the clipping loop of the amplifier such as in the Tube Screamer. The red LED would tell you whether or not the extra clipping diode was engaged or not. In instances like this you would want all of your LEDs to be about the same brightness as it would be a bit offputting to have one noticeably dimmer than the other.