Back when I first started learning digital circuits, the first one would turn on an LED on and off, the rate was controlled by a potenciometer. I had a bit of fun changing the rate to see when the on/off became invisible. With a 'scope hooked up you could see the rate of the square wave.

Fast forward decades, and some friends were working on a portable device with an LED display. It had a power consumption problem. I suggested instead of turning the LEDs on, to strobe them. They'd use much less power, and the difference would be imperceptible to the user.

Then they had the idea of strobing the line of LEDs to form text messages you could see if you waved it back and forth, but was just a line of on LEDs if it was stationary. That worked surprisingly well, but as a toy it never caught on. But it was fun.