[calloc]

You are talking about the PWM frequency. If you are having issues with that make sure to look for a manufacturer that has theirs at 30 Hz or higher, when I worked with LED's we tested that 50 Hz was enough to make sure that humans were unable to see that the light was not constant on.

[lgeek]

I've built LED displays and the lowest frequency at which I wouldn't notice flickering was 500 Hz. This was at 1/8 duty cycle though, so you might get away with a lower frequency at a higher duty cycle.

I find your claim that 50Hz was enough rather strange. Even incandescent light bulbs have noticeable flicker at below 50 Hz and those have considerable warm up / cool down times, as opposed to the LEDs.

[calloc]

Hmmm, it is possible I am doing the math wrong based upon the timer/interrupt on the micro controller and the rows we had...