“How On Earth Do These Light Bulbs Work, Anyway?” The Nuts and Bolts of Those Little Bulbs of Light.

Seth, one of our interns from Oberlin College, did some research about light bulb technology to share with us.  Check it out:

How on earth do these light bulbs work, and how are they saving energy? The underlying principle behind all kinds of light sources is electron photoemission. When an electron in an atom becomes excited, let’s say by an electric current, it bounces up away from the nucleus to a higher energy state and then falls back down to its original position. In falling back down, the electron releases photons, which are little bits of light, at certain frequencies depending on the type of atom that has been excited. This is essentially what happens in a light bulb, but different types of light bulbs perform this task in different ways. In a regular, or incandescent light bulb, a thin metal filament, usually made of tungsten, is the source of photoemission. An electric current is passed through the filament, exciting the electrons in the tungsten atoms and releasing photons, some of which we see as visible light.

A fluorescent light is slightly more complex; instead of a metal filament, electric current passes through a gas mixture of argon and mercury vapor. The excited mercury atoms release ultraviolet light, which then activates a phosphor (the white powder on the inside of the glass tube) producing visible light. Though both types of light bulbs work by the same properties of electrons, their respective media allow for significant differences in the type of light produced and the amount of energy required for them to function. The filament, in order for it to release light, must be heated to about 4,000° F! That’s extremely hot, and indeed most of the light released by the bulb is in the form if Infrared light, which can only be perceived as heat. Only 10% of the light released by an incandescent bulb is visible to the human eye.  On the other hand, fluorescent lamps produce cooler ultraviolet light to activate a phosphor. As a result, they produce more light per wattage of current used than an incandescent bulb; in fact it’s more than four times the amount, and more of the energy is released as light than as heat. That is why a 14-Watt Fluorescent bulb can produce the same amount of light as a 60-Watt standard bulb. Also, they use about a quarter of the energy required for an incandescent bulb and last five times as long. This is how CFLs can save so much energy and last so long. A CFL is simply a fluorescent bulb that has been coiled and mounted onto a base that can fit into the same socket as a regular bulb.

Leaving a 100 Watt incandescent light bulb on continuously for one year would require around 714 pounds of coal to be burned, and in the process of burning would release 5 pounds of toxic sulfur dioxide, 5 pounds of nitrogen oxides (both of which cause acid rain) and around 1852 pounds of Carbon Dioxide. To compare, the average human body produces the same amount of Carbon Dioxide in about 2.5 years. Switching a single Incandescent Light Bulb with a Compact Fluorescent Light Bulb saves around 2,000 pounds of Carbon Dioxide and 16 pounds of Sulfur Dioxide from being released into the atmosphere by using 730 less Kilowatt Hours than a standard Incandescent bulb.