Lateral light-emitting light guides are now widely used in the automotive industry for daytime running lights, tail lights and brake lights. Their aesthetic design and 3D shape are significant recognition factors. They are made of plastic and have a very complex lateral structure which is designed to ensure uniform light emission along the entire length. Among the numerous test criteria in the manufacturing process are dimensional stability, homogeneity, and intensity of the lateral radiation. The measurement of the spectral transmission of the light guide is therefore a key quality test. Uniform light emission over the entire length of the light guide can only be achieved with sufficient transmission. An additional risk is the yellowing of the plastics used to make the light guide. Particularly when used with white LEDs, this yellowing results in a change of the color temperature which is visible to the human eye.
Gigahertz-Optik’s TFCT25 is a test system for measuring the optical transmission of lateral light-emitting light guides, including the influence of yellowing. The system meets all the technical requirements of a renowned automotive manufacturer and therefore holds the status of a qualified inspection device for its suppliers. Besides measuring the spectral transmission and analyzing potential color shifts, the system can also be used for the photometric and colorimetric analysis of LEDs to be used in conjunction with the lateral light-emitting light guides. Its key features include its precision power supply unit for current supply to the LEDs as well as to the meter itself for the operation of the LEDs in both constant and pulsed current modes.