LED question

[J M Fahey]

Those are premade for people who canīt solder a resistor or do the Math; you buy buy spare Leds and add your own resistors.

Most important rating is LIGHT emission; search for the highest mCd (milli Candle) rating possible.

They run from cheap "special of the day" to stupid high efficiency which are to be preferred.

Best is transparent body , NON diffused ones, who project a bright circle on your hand if in front.

[Leo_Gnardo]

I'd like to stock up on some general purpose LEDs. Looking at Mouser, which is more important, forward current rating, or forward voltage? Interesting, they don't offer 9v, it jumps from 7.5v to 12v. They don't have to be high intensity.

What Juan said ^^^. You're looking at LED assemblies, they run say 10x - 25x more costly than individual LEDs. Regular LEDs start glowing typically 1.8 to 3 volts. Wire in a series resistor, any cheap one, and Bob's yer uncle. If you have to replace a cylindrical assembly in an amp, you can choose to buy one of those expensive assemblies to match, or saw the old assembly open & replace the bits inside.

Like Juan I prefer the super brights, you can dim them down with a suitable resistor or run them blazing bright even at a fraction of their rated current. Regular non super brights can be had for small change & even cheaper in quantity. The super brights I get from Mouser typically run about a buck apiece.

Sometimes it is an advantage to have a diffuse lens over the LED, say if you're using one in an effects pedal. That way you can see the LED from the side. Super brights tend to have a narrow cone of dispersion, you have to be nearly on top of them to see. Or, as I said in another comment, you can see 'em cast color beams on a ceiling in a dark room, kool!

[The Dude]

If your ordering, you may want to get some blue ones, also. As I said, they're much more visible in direct sunlight.

[Randall]

I'm still unclear on specs for LEDs.

Taking a look at this datasheet, forward voltage 2 - 2.5v, does this mean it operates in this narrow range, or is this the voltage it turns on at? If it is the latter, how do you know how much voltage is too much? Or is it current that matters?

Speaking of current, this one has max current 150mA, with steady current 30mA. Is this what it normally draws, or are these max values? Will it still light up if the series resistor drops the current down to 10% or so of 30mA?

I want to get some differnet ones and bread board them to try to better understand how to safely design them into pedals and other projects without blowing them up or causing undue battery failure.

I have a few in a bag that I wrote green 3.3v 20mA, and red 2.5v 20mA, but I forgot what that means.

https://www.mouser.com/datasheet/2/2...ID-1137579.pdf

[Enzo]

That means the diode has a forward drop of 2-2.5v, just as a 1N4007 has a forward drop of about 0.6v.

You determine what it draws. Consider the 2v forward, then consider the power supply. You then calculate what resistor in series would serve the 2ma.


The 20ma you wrote was probably from their data sheet, and that would be the max curent to draw from them.

You can take an LED and run it through a pot from a battery. You then visually see how bright it gets. Find a brightness you like, then measure your pot setting. Then find a resistor close to that value.

[Randall]

Ok, voltage drop, that makes sense. So does max current. I breadboarded a couple with a pot and did that experiment, which ended in excitement. The clips on the pot touched, and the top of the green LED blew off like Krakatoa with a loud crack and a foul smell! It was powered by my 2A DC supply set to 9v. On the second try I found a reasonable brightness at ~ 2mA with a 3K resistor, measuring 6.2v across the pot. It's making sense now.

[Leo_Gnardo]

a loud crack and a foul smell!

You da mad scientiss! Careful with those LED's some are based on a substrate containing arsenic. Don't worry, a little in the air won't hurt, but don't want to repeat the experience. Like with selenium rectifiers. Bad stuff.