Coding:

Stroboscope

A dark room is recommended, with your eyes closed and the screen fairly close to you. It starts off flashing at a frequency of 10 Hz. Click or tap the screen to cycle between 8 and 12 Hz.

Warning: This kind of flashing is not safe for people with photosensitive epilepsy. Use with caution. If you understand the risks, go ahead and start it up.