Persistence (of phosphor) - Display devices

Time it takes the emitted light from screen to decay to one-tenth of its original intensity. The point where an electron gun strikes the phosphor coated screen starts glowing and maximum brightness is observed on the focus (strike) point of the electron gun. The brightness tends to reduce radially as per the Gaussian distribution. Actually at the gun strike point the energy level of phosphor atoms is highest and gradually spreads over the nearby phosphor atoms. The 'original intensity' is the maximum brightness that is achieved when the electron gun strikes the phosphor atoms and the corresponding electrons reach maximum possible 'excited state'. In order to keep the pixel glowing, one requires to re-strike the electron gun on the same point before the screen point fades away, that is, before the energy level of the phosphor atom reduces to a certain limit as defined in the term persistence.

This is known as refreshing of the pixel. Infact the rate of refreshing depends on the type of phosphor used and also on the human perception limits. Before the human eye could catch that the pixel is beginning to reduce its intensity, the pixel must be refreshed. In CRT monitors, the entire screen frame is refreshed normally 30-60 times in a second. This is called refresh rate. Lower persistence phosphors require faster refresh rate and higher persistence phosphors require lower refresh rates. The lower persistence phosphors are used in monitors that are specially designed for animations, whereas higher persistence phosphors are mostly used in complex static representation of objects such as in CAD/CAM (Computer Aided Design/Manufacturing).