LED Research and Useful Sites

July 22, 2008

Resistor calculator for LEDs

How is LED Brightness related to current?

So let’s review what’s typical: for 3mm and 5mm indicator-type LEDs, datasheets often list a typical forward current of 20mA. Forward voltage will depend on the junction material of the LED, but let’s use a white LED as an example. 3.3V would be a typical forward voltage at 20mA. So applying the series resistor calculator, we get a curent-limiting resistor value of 85 ohms (100 is the next largest standard value), and a power dissipation in the LED of (3.3V * 0.02A =) 66mW.

Very detailed info on LEDs – everything you ever wanted to know

Gizmology – general LED info
Infrared LEDs info

Luminous flux = amount of light being put out

Brightness vs. viewing angle
Keep this in mind when buying LEDs for illuminating purposes – a 2000 mcd 30° LED puts out just as much light as am 8000 mcd LED with a 15° viewing angle. (The angle is half in both width and height, so the beam is four times as bright.) This is one of the reasons that ultra-bright LEDs are often “water clear”, to keep the light going in one direction and not diffuse it all over the place.


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