ericgibbs, the 25-30hz is incorrect, it depends on the modulation depth and off time vs on time and the relative motion of the observer and object, many people can easily see flicker at 120+hz if it's 50-50 duty cycle and on off modulation, such as with LED arrays run directly off AC power. or PWM'd with a high off to on ratio. For LEDs to avoid flicker I wouldn't use anything less than 200hz, higher if available. The flicker is especially noticeable if the object is moving.