FLICKER FUSION FREQUENCY

The Light Rays you see in these images occurred due to the fact that the flicker fusion frequency of the observer has been exceeded.

Flicker fusion frequency can be defined as that frequency of a flicker (of light) which is higher than the frequency of perception of vision of an observer(e.g. Human, fly, camera)
It is that critical interval at which a flicker of light will appear to FUSE into one continuous ray of light.

ILLUSTRATION
In patterns/signs formed by arranging small led bulbs in a given shape and programming them to turn on sequentially from one end to the other (e.g. In led bill boards or commonly seen in filling stations- WELCOME TO OUR FILLING STATION). This creates an illusion to the observer, making him think the lights/letters are actually moving. If you increase the speed at which each light comes up, your eyes will deceive you into thinking you're seeing rays. This is because the frequency has exceeded the FLICKER-FUSION FREQUENCY of your eyes.(i.e. the lights are moving faster than your eyes can process it due to a phenomenon known as THE PERSISTENCE OF VISION)

Now for flies, their persistence of vision, last longer than humans; this results into a flicker-fusion frequency that is much higher than ours, hence, even when we wave our hands to kill them- they will see our hand motion as slow moving rays, then they take off.

This also explains why High Speed/High Definition Cameras are needed to video car races to avoid blurred videos.

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