Philips has a patent on a way for cellphones to provide their owners with precise, real-time advice on safe exposure times for sunlight. This all tailored to a specific location. For this the cellphone network uses its own UV sensors or sensors belonging to meteorological departments. The cellphone network knows roughly where a cellphone is, so it can send users up-to-the minute UV index ratings based on current locations.Together with the factor of the suntan lotion the cellphone can display the safe exposure time.
more information:
US patent office