Fire and Light Bulbs

The most ancient of discoveries and the epitome of invention, fire and light bulbs both provide light by the same process: incandescence.

In fire, from forest fires to Bunsen burners, chemical reactions release heat, releasing gases and raising materials to high temperatures, where the gases and materials incandesce. Depending on the reactants, different temperatures are produced resulting in different colors. Also, certain chemicals can tint the color of the flame. In a Bunsen burner, the reactants are primarily methane (CH4) and oxygen (O2). The products are also simple: water (H20) and carbon dioxide (CO2). When you look at the flame from a Bunsen burner, you can see different sections with different colors. These differences are due to variations in heat (the hottest point is the tip of the inner cone) and also the chemicals being heated. In forest fires by contrast, the reactants are organic molecules in the wood. These are fairly complex with many portions being incombustible, so the product of the fire contains many impurities and the fire is much cooler. Thus, wood fires tend towards orange-yellow, or reddish when they die out.

Light bulbs also produce light through incandescence, but they use electricity to produce the heat. Inside a light bulb, as in electric coil heaters, electrical current runs through a thin wire and heats the wire to a high temperature, causing the wire to incandesce. Brighter (and whiter) light requires higher temperatures, which in turn require more electricity. You can figure out how much energy is being used by a light bulb by looking at its watt rating. A watt is equal to one joule of energy per second, so a 100 watt light bulb uses 360,000 joules an hour, enough energy to lift a ten kilogram (22 pound) object 3600 meters (2.3 miles)!

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