The torch (British English) or flashlight (US English) is a simple tube containing two batteries (cells) end to end and linked to a small bulb in a series circuit. There is also a switch to make and break the circuit. Behind the bulb is a shiny curved reflector mirror. The shape of the mirror is designed to produce a parallel beam of light.

The traditional flashlight/torch is being replaced by LED versions today. These use less power and so batteries last longer. They can also use smaller batteries, and so are lighter to carry. Each LED is covered with a lens that directs the light. A combination of different lenses makes the light from a bank of LEDs form a parallel beam.