Why did the numbers 1234 on the seven-segment displays begin to display normally only after adding a delay?

Question

Arduino

https://www.youtube.com/watch?v=9oxvl-9pz-c&t=1898 31:38
Why did the numbers 1234 on the seven-segment displays begin to display normally only after adding a delay (further in the video will be done)?

Answer 1

It is connected with dynamic indication most quickly - the segments do not have time to go out during fast switching due to transients ...

Answer 2

It takes time for the LED to reach its full brightness. If you turn it on and off too quickly, it will shine, but too dimly.

Answer 3

Physics of the LED, radiation inertia When receiving additional energy, the electrons move to a higher energy level where they cannot stay for a long time and descend, releasing excess energy in the form of a photon. When the supply of external energy (power) stops, some of the electrons continue to emit photons for some time.

Answer 4

Alternately switching sections 10-13 to 2-9, the signal of the previous digit remains, so each digit is displayed on two indicators.