ighting at night. The variation in brightness is achieved as follows:
The liquid zone appears significantly dark during operation due to the refraction of most light rays inside the liquid, resulting in an almost black appearance because the non-reflective gauge chamber interior prevents the refracted rays from being externally visible.
In contrast, the gas/vapor zone appears nearly silver due to total reflection of light rays at the glass/gas-vapor interface. This reflection, causing a 90 turn,