Quote Originally Posted by flotulopex View Post
Thanks a lot for your information.

In my case, I think it will not be mandatory to pulse anything.

Let's make it simple, no?

Thank you anyway.
Sounds like a perfect place to put a PIC10f200. 6 pins, no oscillator; power, ground, switch input, LED output, and still 2 pins left over to play with.
Program changes the PWM to the LED according to the switch input. Easily done.
About the only thing I can see needing to be done outside of that would be to add an external MOSFET to switch power to the LED, but that depends on the total current your LEDs are pulling.

The rest of the guys are right though...
PWM at V(f) at near maximum I(f) on an LED is the only way to go. There's just too much variation in brightness to be messing with different current limiting resistors. If you look at the spec sheets and the graphs for the light output from the high brightness LEDs, you'll see that the majority of LEDs are only spec'd to run at X amount of current to produce Y amount of light. Lower current levels generally aren't even listed because there's just too much variation. PWM is just that much more efficient, produces less heat, your eyes don't know the difference...etc.etc.etc.