Difference in Heat Between Incandescent & Fluorescent Bulbs
The 21st century affords the option of purchasing incandescent and/or fluorescent light bulbs for our homes. The bulb varieties are considerably different in construction, in mode of operation, and in energy-to-light efficiency.
Early fluorescent bulbs were lengthy tubes. The modern "compact fluorescent lamps" (CFL) are shortened and sometimes coiled to fit incandescent fixtures.
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Incandescent Bulb Construction
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Most incandescent bulbs are very simply constructed. Inside a glass envelope is a sealed vacuum to exclude oxygen. In the middle is a thin metal filament of high melting point, often tungsten. Electricity is passed through the filament. The wire has high resistance, so it becomes very hot and it glows quite brightly, producing light. The lack of oxygen prevents the filament from burning out. Still, it emits large amounts of heat, and that represents energy not used in producing light. The construction is simple. The cost is inexpensive.
Fluorescent Bulb Construction
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The fluorescent bulb is coated on the inside with a phosphor. Rather than a vacuum, the tube contains a low-pressure mixture of argon and mercury. A combination of filament and "ballast" initiate and regulate electron emission and light production.
Electrons passing through the gas "excite" mercury atoms. Some of their electrons undergo "orbital transitions" to higher "energy levels." This unstable situation lasts only briefly and the atoms re-emit energy but in the form of ultraviolet light. This invisible light is the reason the tube is coated with phosphor. Ultraviolet light strikes the phosphor coating, which converts it into the visible light we see.
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Why Resistance Matters
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Combining two well-known physics equations, namely, Watt's Law and Ohm's Law, we obtain an equation in which power consumed is P, current flow is I, and resistance to that flow is R,
P = I²R
Notice that the current I is squared or is multiplied times itself. If the current use is merely doubled, the power consumed is four times as great! That's four times the money spent. Since the resistance in a fluorescent bulb is much lower, a lot less current is consumed. Although the cost of fluorescent bulbs enters into the figuring, it is possible to get the same amount of light at considerable savings in electricity.
Efficient Light Production
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A fluorescent bulb contains low resistance gas for electric transmission, rather than a high-resistance filament. For this reason, the fluorescent bulb produces very little heat and uses far less power. It is efficient. While it is true the incandescent bulb generates lots of heat, that isn't always a bad thing, however, and during colder weather the warmth of incandescent lighting may not be unwelcome.
Concerns
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Persons concerned with our environment seek alternatives to wasteful technologies and ways of life. This is good; however, there are considerations that go beyond the pocketbook, and beyond mere waste. Although high-quality fluorescent bulbs may be 70 percent more efficient than their incandescent counterparts, they contain mercury. Disposal methods are not convenient. Spent bulbs break. They wind up in the trash, the landfill, and eventually, in the water supply.
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References
Resources
- Photo Credit Spiral Compact Fluorescent Lamp; Kevin Rector: commons.wikimedia.org
