6B40.10-Light on a Variac

6b4010light on a variac
Description: This demonstration shows how the color of light emitted from an object changes with temperature.


  • Overhead projector light
  • Variac
  • Variac to banana plug cable
  • Table clamp
  • S clamp
  • Medium length rod
  • Vertical filament light bulb

Setup Procedure:

  1. Mount the light on a pole and attach to a table.
  2. Connect the light to the variac.
  3. Test to make sure it works.

Demonstration Procedure:

  1. Turn off most (or all) of the room lights.
  2. Turn on the projector light.
  3. Slowly increase the voltage and note the change in color of the bulb. It will start off as a dark orange, and progress its way to a bright white.
  4. Do not leave the light on for very long since it gets very hot and can break. When finished, turn the light off.