light pen

1. N a rodlike device which, when applied to the screen of a cathode-ray tube, can detect the time of passage of the illuminated spot across that point thus enabling a computer to determine the position on the screen being pointed at 光源路径诊断系统

2. N a penlike device, used to read bar codes, that emits light and determines the intensity of that light as reflected from a small area of an adjacent surface (用以阅读条形码的)光笔