Electroluminescent materials are fast becoming a very common feature in today's world, from aeroplanes with electroluminescent lights that guide you to the nearest emergency exit to illuminated EXIT signs.  These work by giving out light when an electric current is passed through them. Light released at specific wavelengths is absorbed by the material, specifically the photons in the light. These photons are then re-radiated and give out a special luminous light.  Luminescence is used in many products from watch faces you can see in all types of weather to paint, lightbulbs and even in forensic detection to trace fingerprints to track down the culprit.