Why is the glass components of all Geiger tubes painted black?
The reason is to prevent the Geiger tubes from being light sensitive. The sun is an excellent radiation emitter and as such if a Geiger is used externally as a probe for example with no case protection the Geiger would be light sensitive if the glass was not paint black. This is not an important issue if the Geiger is fully enclosed in a light tight box. In these applications unpainted Geiger’s can be used.
