välkkymistä

Välkkymistä, often translated as flicker or shimmering, is a visual phenomenon where a light source appears to rapidly change in intensity or color. This can occur due to various physical and physiological reasons. In physics, flicker can be caused by fluctuations in the electrical power supply to a light source, such as those encountered with alternating current (AC) where the voltage and current oscillate. Incandescent bulbs, for instance, can exhibit flicker as their filament heats and cools with the AC cycle. Other causes include atmospheric conditions, like heat haze distorting distant objects, or the rapid movement of an object in front of a light source.

From a perceptual standpoint, flicker can also be a consequence of how the human eye and brain process visual information. Some types of displays, particularly older cathode ray tube (CRT) monitors, refresh their images at a certain frequency, and if this frequency is too low, viewers may perceive a noticeable flicker. This can lead to eye strain and discomfort. In some natural phenomena, such as the twinkling of stars, perceived flicker is due to atmospheric turbulence that refracts and scatters the starlight as it travels to Earth. The term välkkymistä is a general descriptor for this visual effect across these different contexts.