In reflex gauges，the fluid is viewed through a reflex glass, a crystal with a smooth surface and a prismatic surface.
The action of the refraction allows to see the internal level of fluid, considering that in its liquid fase totally absorbs the light and makes the fluid appear dark. The one connected with the gas/aria totally reflects the light and has a clear color.
The reflex level gauges offer many advantages such as a low purchase and maintenance cost and an easy level reading.
However they cannot be used in certain cases, for example when the separation level between two liquid must be read；when the observation of the liquid color is required or when the fluid is high-pressure water stream.