BSL Physics Glossary - light sensor - definition
When light falls on this sensor it changes to electrical energy. For example a street light has a light sensor on its top. The light sensor works in the night and the day. Let's say it's daytime. There is a lot of light coming into the sensor so the electricity is turned off. At the end of the day as it gets dark, the amount of light energy coming in to the light sensor decreases, and that means the electrical current is turned on to light the lamp. So the sensor controls the electrical supply.