LED Question(diode)

What current do I need to get an LED going?

I have a 12V circuit, so what resistor value should I put in series with the diode so it emits good light?

Thanks!

-D

Depends on the LED. What is its maximum forward current? What is the voltage drop across it?

If you want a generic number, I've heard that 20mA is a good current value. Ignoring the voltage drop across the LED, 600 ohms would give 20mA, so a 620 or 680 ohm resistor should be safe. Try that, and, if it's too dim, go with a smaller resistor. Recognize that, if the resistor is too small, the LED will burn out.

Answer 560 ohms 1/4W 5%

Solution

Typically the LED runing current (I) and forward voltage (VF) are

20ma (0.02A) and 2V respectively. Voltage Source (VS) in your instance is

12VDC

Formula for the Resistance

R=(VS-VF)/I

R=(12-2)/0.02

R=10/0.02

R=500 ohms next standard resistor 560ohms

Wattage calc Power (P)= Voltage (V) x Current (I)

P=VxI

P=10x0.02

P=0.2 watage rating can be 0.25 or 1/4watt

Always round your result up to the nearest standard value. You can mess with the current too get more brightness but don't go higher than 30ma typically.

My brain hurts!

And in case you need it, there are online calculators for this sort of thing. One is here. A Google search for led resistor calculator will turn up more.

My calculator is here:

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

Most LEDS have a max current of 20ma but you can get by in a pedal with much less... 5ma at most and with an efficient LED, 2ma will do the job.

regards, Jack

Holy geez! Answers galore ! Haha

Thanks alot guys!

BTW: Where to find those LED chassis cradles?

-D

Do you have a place where you get your LED's?

-D

I buy the LED mounts from some guy on Ebay. He sells them all the time for low prices.

The LEDs came from Ebay also. There are numerous suppliers with better rates than the usual electronic outlets.

regards, Jack

i get LEDs from china/thailand on ebay. you pay like $3 + $4 shipping for 100 or so LED's plus resistors, every once in a while there will be a dead one, but for the most part they work fantastically, just have to wait a week to get em.

Damn, I found a couple LED mounts, but they seem to fit smaller chassis thickness... I need something to fit my thick chassis!

-D

20 mA is a good rule of thumb, but 20 mA through a blue or green will stab you in the eye when you look at it straight on. At 12 V, a 2k2 resistor will give you about 4 mA and is about right, still clearly visible in full day light.

I have also found if you take some sandpaper and rough up the clear lens, it softens the light a bit and increases the viewing angle.

I have never been happy with those 2 part LED holders. I have had some success with welding the 2 parts together with my soldering iron.

I was thinking about over-intensity... Like a laser beam slamming into your eye and causing burnt retina syndrome. So 5ma seems like the golden current

-D

If you want to be really cool, customize the color with a dab of nail polish or acrylic paint.

I was thinking about over-intensity... Like a laser beam slamming into your eye and causing burnt retina syndrome. So 5ma seems like the golden current -D

There really isn't a magic current number. It depends on the color of the LED, the type of lens, and the visible light angle.

If you've got an assortment of resistors, just try different ones until you get a comfortable brightness. I tend to limit the current to keep the LED fairly dim, but I build mostly pedals where battery drain is a consideration. I find that about 7ma through a red LED is good for my purposes.