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Light Bulb Challenge

Use this simple experiment to test whether new light bulbs are really more energy efficient.


  • incandescent bulb, 60 watts
  • compact fluorescent light (CFL) bulb, 15 watts
  • 1 desk lamp, shade included
  • 1 Tbsp cooking oil
  • 1 dropper
  • 2 half-sheets of paper
  • ruler
  • 2 books of equal thickness
  • stopwatch or clock
  • paper and pencil


  1. Start by making a bridge with a half-sheet of paper and books and placing the lamp with an incandescent bulb about 6 in. from the paper.
  2. Have your girls place 1 drop of oil on the paper, and quickly measure the initial diameter of the oil circle.
  3. Turn on the lamp and observe for 5 min. Measure the final diameter—quickly! Then subtract the initial diameter from the final diameter to find out how much the oil spread.
  4. Repeat this experiment, substituting the CFL for the incandescent bulb.
  5. How do the oil circle diameters from each light bulb compare? (Incandescent bulbs give off more heat than CFLs, causing the oil to spread farther. They also require more energy because most of the energy is lost to heat.) Have each family member try placing their hand under each bulb for a few seconds. What do you feel?

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