How Does a Flashlight Work

Whether you’re outdoors for a nighttime adventure or find yourself in the dark from a power outage after a storm, the convenience of portable light is as close as a simple button on your flashlight. But just how does a flashlight work?


1 – Case   Usually plastic or metal tubing that holds the batteries (dry cells) and the circuitry of the flashlight

2 – Springs (and Contacts) A very thin spring (or strip of metal (usually copper or brass)) that begins at the bottom of the flashlight and runs through the length of the light, connecting the batteries with the switch and the bulb. This “hooks up” the complete flashlight circuit.

3 – Switch   The part that completes or breaks the circuit based on its position. When thrown in the ON position, it moves a metal part into position to complete the circuit. When thrown in the OFF position, that metal is removed from the circuit, stopping the flow of electricity.

4 – Reflector  A reflective layer, usually made of aluminum, or aluminum coated on plastic, that focuses the light emitted from the bulb in one direction.

5 – Bulb  This is the component that produces light. In older flashlights, an incandescent bulb was used as the light source. This technology relied on a filament made from tungsten to heat up by the resistance of the flow of electricity through the filament to create light. Today, light emitting diodes (LED’s) are the more common form of bulb used. LED’s are considered to have no expiration, whereas incandescent bulbs will burn out and need to be replaced.

6 –  Protective Glass  More often made from plastic, this part keeps the bulb separate from outside conditions. In many cases, this component also has properties that focus the light further and sometimes helps magnify the light.

7 – Batteries (or Dry Cells)   The power source for all portable lighting devices.