A device operated by daylight, that automatically controls a light source, lighting it at or about sunset and extinguishing it at or about sunrise.
Note: If the light source is an electric lamp the device is called a sun switch.
If the light source is a gas flame or a gas mantle, the device is called a sun valve or light valve.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
nertia of the water plane
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM