Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

Halogen bulbs versus ordinary bulbs

This project must be done by individuals.

Light bulbs come in a number of varieties. Ordinary bulbs contain a tungsten filament surrounded by an inert gas such as xenon. These bulbs are designed so that the filament reaches a temperature of about T1 = 2500 K.

Halogen bulbs, on the other hand, place a halogen gas, such as bromine or iodine, around the filament, and encapsulate both within a small quartz envelope. Chemical reactions between tungsten atoms which evaporate from the filament, the halogen gas, and oxygen in the quartz, cause some tungsten atoms to be deposited back on the filament. This extends the life of the bulb and allows it to run at a higher temperature, perhaps T2 = 3000 K.

Which bulb is more efficient? Let's use this definition of efficiency: the fraction of all radiated energy which lies in the range visible to humans.

  1. What is the range of wavelengths visible to humans?
  2. What fraction of an ordinary bulb's blackbody radiation falls within this range?
  3. What fraction of a halogen bulb's blackbody radiation falls within this range?
  4. How much more efficient is a halogen bulb?

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.