For an LED that is rated at 20mA, is it safe to PWM it at 40mA half the time? Will that make it nearly as bright as if continuously supplied with 20mA?
Thanks Olin and tcrosley for your answers. I didn't want to distract from the question by adding the details of what I am doing, but here it is:
I am working with an LED strip from http://www.environmentallights.com/LED-Strip-Light-Double-Density-4-Wire-Red-Green-Blue-by-the-5-meter-reel_P3846.aspx. They do not have a datasheet per se. I think the LEDs are connected as shown in this image http://www.ladyada.net/wiki/_media/products/ledstrip/astripsch.png.
Based on what I read about LEDs in general, 20mA per color seemed safe. I tested it - using 12V, potentiometer and 3 inches long strip, that is 3 leds in series each color - for short periods, few minutes, and 20mA per color seems to have worked fine, good enough brightness and no overheating or color intensity variation.
I will be working with up to 2 feet length strips, that is 160mA per color and 480mA to get White. I may have up to 10 strands to control. That will add up to about 5Amps. I will be using the Propeller microcontroller from Parallax to flash the strips in various patterns and colors. Will use mosfets to drive the LEDs.
I was thinking of supplying about 200mA instead of the 160mA needed per color, but then I will PWM the leds such that only one color is on at a time; at a frequency of 1KHz. So to get white, each color will be on for one third the time, that is 0.3 msec. At any moment only one color is on, only 200mA is drawn. I imagine the leds will be less bright, hopefully not by much.
So, for 10 strands, I will deal with only 2A instead of 5A.
Please let me know if what I am thinking is off.