How Does a Night Light Work?

A night light is a small, low-power electric light kept on at night for comfort and safety. They provide enough light to see the outlines of objects in a room, but are dim enough to not disturb your sleep. Night lights are often used to comfort children who are afraid of the dark.

The Basics

They can also be used in hallways and bathrooms to allow people to navigate the house at night.

Simple Night Lights

The simplest night light is a small plug-in device with a low-watt incandescent bulb and a mechanical switch. The switch works like any wall switch, connected to wires that complete an electrical circuit. It turns the light on and off.

Automatic Night Lights

Many modern night lights are designed to turn on automatically when it gets dark and turn off automatically when it is light again. They use a detector called a CDs cell. A CDs cell is a type of resistor called a photoresistor. Resistors resist the flow of electricity. Photoresistors differ from other resistors in that they change when light shines on them. When light shines on a CDs cell, it decreases the resistance. The night light has a detector circuit which automatically turns on the light when the resistance reaches a certain level. High resistance means that there is no light shining on the CDs cell, so the night light turns on.

Efficienct Night Lights

Incandescent light bulbs are very inefficient. Since they work by heating up a wire, most of the electricity they use is turned into heat energy instead of light. Some modern night lights use light emitting diodes, or LEDs instead. In LEDs, electrons are forced to jump a gap between two different materials. When the electrons jump the gap, they release a little bit of energy in the form of a photon of light. LEDs make very little heat, which means they waste very little energy.

The Drip Cap

A night light is a small, low-power electric light kept on at night for comfort and safety.
They provide enough light to see the outlines of objects in a room, but are dim enough to not disturb your sleep.
When light shines on a CDs cell, it decreases the resistance.
The night light has a detector circuit which automatically turns on the light when the resistance reaches a certain level.
Some modern night lights use light emitting diodes, or LEDs instead.