Super Bright LED question

[nirvanas silence]

I got a few super bright LEDs from smallbearelec.com and I don't have a spec sheet.  So could anyone tell me what the lowest resistor I can use with a 9V battery without damaging the LED?  Thanks alot.

[petemoore]

or lower. for brightest...
 I think you can measure the current going through it.
 I can tell how bright they 'want' to go [usually].
 Too much current and your LED will take it only so long.
 Formula..that's right..welll anyway I dont know the math for that.

[MarkB]

I picked up a batch of 100 VERY bright blue LEDs (cheap!) - and I blew up 2 of them while figuring out the proper resistance...  I was using the 'hook up a pot in series' trick, but apparently was using a small pot that went too quickly from 'ok' to 'pop'.

I ended up using an 8k2 resistor for it, which kept it from being TOO bright.
"-)

[bobbletrox]

I use a 4k7 on super brights.  They're still pretty brilliant that way.  Any dimmer and they have that 'dead battery' look IMO.

[bobbletrox]

Use a really low value resistor and turn your LED indicator into the Bat Signal.

[AL]

Here's a good LED wiring page:  http://www.caving.org.uk/gear/led/wiring.html

And here are some super bright spec sheets:
http://www.superbrightleds.com/

I like the Bat Signal idea.

AL

[nirvanas silence]

Thanks, i was going for the absolute brightest possible without damaging.  I am gonna see how the 4K7 does.

[Samuel]

i use a 470 ohm. I'm still seeing spots from a pedal i gave away as a christmas present. :shock:

[Rick]

It depends on the led in question. Are your leds those clear blue superbrights ? If so from looking at the above spec sheets the led current is often 20ma and the forward voltage is 3.5vdc for the superbright blues. If you want to max out the led and maybe make a little flashlight with it you could do this. I make no claims to it's accuracy.
First subtract the led forward voltage from the power supply - in this case it's 9vdc. So 9v - 3.5v = 5.5v  Now just use OHMs law to get the resistor.
I=V/R or .02amps = 5.5v/R  or .02R = V  so R = V/.02  giving you R = 5.5v / .02amps = 275 ohms. This is the max suggested operating current for the led for high brightness apps. Look down the led barrel for a sec for a near laser - brain drilling experience. You may want to design for a less bright led with higher resistances to limit current as you see fit, but you won't shorten the led's life span much with 9v and around 270 or so ohms.
Check the spec sheets for the forward voltages (voltage drops I believe) for other led types and calculate the resistor the same way.
I believe this is accurate but gurus please step in with more info.
(I haven't blown any leds with this approach ...yet)

[idlefaction]

i use those 4000mcd blue superbrights too, i started out makin them as bright as but now i use 10k's with them.  20mA will actually drain a 9V pretty quickly...  if you use a 470ohm resistor you'll probably expect to get a couple nights out of a 9V just for the LED alone.  with a 10k you can play the same battery for months, and it still lights up the stage  

ymmv...

[bobbletrox]

That's a 1500mcd blue LED with a 680ohm resistor.  The picture on the right is the ceiling above the pedal.

[zachary vex]

that's silly.  i use 22k resistors in series with my leds to save battery life.  what are you thinking?  even a 1k will draw a full 10 mA from a new carbon-zinc battery... that's as much as you need to operate a lo-fi loop junky!

[bobbletrox]

I didn't keep it like that of course  :wink:

[smoguzbenjamin]

That's pretty cool when you're in a smokey gig though, big beams of blue light coming from your pedalboard :mrgreen: I should make that on my guitar!

[ErikMiller]

that's silly.  i use 22k resistors in series with my leds to save battery life.  what are you thinking?  even a 1k will draw a full 10 mA from a new carbon-zinc battery... that's as much as you need to operate a lo-fi loop junky!

I share Zach's politics regarding current draw.

With the BRIGHT blue LED's I use (besthongkong.com), I can stick a 22K in series and be able to read using the light from the pedal.

It's an indicator, not a Nose Hair Illuminator.

[Ansil]

question then what if you only use a power adaptor for the thing... i am not saying to read stuff of the ceiling with it but if the person only uses adaptors they why bother if you have like a 2A available powersupply

[The Tone God]

If you got the power to spare then go ahead and waste it making light. My only concern at that point would be running the LED too bright that you diminish its life span. Well that and pehaps the circuit you might be driving the LED with.

With a battery you have a "power budget" that you have to work with in. I agree that using current just to have a stupied bright LED is silly and wasteful. Pedals should be designed to help prevent the onslaught of batteries going into landfills. Let be enviromentally concensous here. I've built some effects that are passive that don't require power sources. I even built some effects that are solar powered.

Andrew

[Quackzed]

anybody try super bright leds as clippers?.... it would be cool to mount one on top of a stompbox and watch it light up and dim along with your playing....like a tiny color organ or light organ like on jukeboxes...disco city!!! lol even if you used a sidechain just for the led light up effect...that would be cool huh huh ...huh huhuhhuh... too cheesy?... just a thought...

[RDV]

anybody try super bright leds as clippers?.... it would be cool to mount one on top of a stompbox and watch it light up and dim along with your playing....like a tiny color organ or light organ like on jukeboxes...disco city!!! lol even if you used a sidechain just for the led light up effect...that would be cool huh huh ...huh huhuhhuh... too cheesy?... just a thought...

Yes, and it is neat to watch in the dark, but they don't get that bright.

RDV