pwm msp432 led blinking
Since you appear to be concerned with flicker- If there is relative motion between the light source and your eye, the image may appear to "break up". The sensors in your retina act as if they integrate over a period of time in the milliseconds, but you can see a much more brief flash- it just appears dimmer for shorter durations below the flicker fusion frequency. For example, if you whack yourself over the head with a book you may be able to see a 1kHz flash break up, but the camera frame rate will at best do some aliasing thing with the shutter speed unless it is a high speed camera. This is not a coincidence, the camera frame rate is made just fast enough to appear steady, which is much slower than what can be picked up with persistence of vision. Flicker is also more perceptible in peripheral vision, 100Hz is annoying for many people- probably an evolutionary adaptation to help our ancestors pick up rapid motion of predators or prey out of the corners of our eyes.

If there's no motion the light may appear steady above some frequency in the tens of Hz, but it will vary a bit with duty cycle, I think, probably getting somewhat worse as the duty cycle gets shorter (due to the logarithmic response). Above the flicker fusion frequency perceived brightness is lower for lower duty cycle, so a 10% duty cycle source needs to be 10x brighter to be perceived the same as a light source at 100% duty cycle.