alternative current

For lamps, the filament is heated up to produce heat, and finally light. The heating/lighting effect is too slow to react with the 50Hz.
For florecent tube, the light is actually "flashing". The frequency is 100Hz instead of 50Hz, due to the sinusoidal wave form (peak at both positive and negative) If you have a light sensor, you can see the flashes. For record player (turntable 唱盤) in the old days, there is marking on the side to see if the speed is correct, it only work under florecent light. Similarly, a whipping top (陀螺）with pattern spinning under florescent wll produce some funny effects, but not sunlight (which does not flash)
If you have a webcam, and set it as 60 frames per second (60Hz), you can see there is ripples in image in florescent lighting, it is due to the flashing (50Hz) is not syncrhonized with the frames.
The most interesting could be your old CRT TV. WHich is actually flashing at 25Hz. Cleverly interlaced with alternate field and make it effectively as 50 frames per second. However, at very bright area, you can still see the falshing. But since the eye is slow responding to flashing. If the flashing is at above 24Hz, you don't see it. It is widely known as Persistence of vision (視覺暫留)