As a child, my favourite four words were ‘glow in the dark’. I decided to find the answer to an almost lifelong question; how does it glow?
Things glow in the dark contain phosphors, which when ‘charged’ by a light source can reflect that light for around ten minutes. They are present in fluorescent lights, in which case ultraviolet light ‘charges’ the phosphors to make it glow brightly.
There are many types of phosphors out there, but zinc sulphide and strontium aluminate are mostly used in the production of toys. In plastic toys, the phosphors are mixed in to the plastic before being put in a mould.
There are, however, ways to keep the glow in the dark items glowing. Some watches with phosphors in the clocks hands have radioactive elements, keeping the hands glowing without the need to be charged.