Indicator for indicating the presence of a liquid

摘要

A description is given of a rain indicator (1), which has a light source in the form of a light emitting diode (36) and a light detector in the form of a photodiode (37). There is a light guide (20) made from a material transparent to the light of the light source and e.g. glass, which has at least one surface portion (45, 46) exposed to the precipitation and which is so positioned relative to the light source that the light source light is totally reflectable towards the light detector on the surface portion. When the surface portion is dry light passes by total reflection to the light detector. In the case of precipitation a gap (43, 44) adjacent to the surface portion fills with liquid and the light intensity is substantially coupled out of the light guide (20) and no light passes to the light detector. Total reflection again occurs when the gap dries out.