Skip to main content

The National MagLab is funded by the National Science Foundation and the State of Florida.

Arc Lamp

Arc lamps were the first type of electric light, so brilliant the lamps were used for lighthouses and street lights.

An arc lamp produces light when a high current crosses a gap between two conducting electrodes, usually carbon rods. English physicist Sir Humphry Davy invented the arc lamp in the early 1800s by using charcoal sticks and a battery to create an arc across a 4-inch (100 millimeter) gap.

Let’s take a closer look at how it works.


  1. Observe the set up of two carbon rods, connected to opposite poles of a battery
  2. Use the slider to move the rods together to close the gap, creating a circuit
  3. Slide the rods slightly apart to allow the current to jump across the gap, creating an arc
  4. Continue sliding the rods apart to enlarge the arc
  5. Keep widening, the arc will stop when the gap is too wide for the current to jump

High resistance as the current struggles to jump the gap sparks the bright light, and creates intense heat of up to 6,000 degrees Fahrenheit (3,315 degrees Celsius).

The tricky part of such arc lamps is getting them to stay on. The carbon rods gradually burn down, so the gap must be adjusted constantly. In this example, an electromagnetic mechanism moves the rods to maintain the gap size and keep the arc burning.

Today, arc lamps are used in applications requiring intense brightness, such as searchlights, floodlights and large film projector lights.