Definition of the word light pen

The term "light pen" originally emerged in the late 1960s to describe a special type of input device that could be used in conjunction with a cathode ray tube (CRT) display, such as a television or computer monitor. The device consisted of a handheld pen with a photodetector, which was sensitive to light. When pressed against the CRT screen, the photodetector detected the light emitted by the phosphorescent coating on the screen's surface and generated an electrical signal. This signal was then converted into a coordinate and communicated to the computer, allowing the user to select and manipulate on-screen entities or make other types of input. Thus, the "light pen" enabled greater precision and interactivity in computer graphics and user interface design, paving the way for the development of modern graphic tablets and touch screens.