Light bulb design
Light bulb design encompasses the technology and principles behind the creation of electric light sources, primarily focusing on incandescent and compact fluorescent bulbs. The evolution of light bulbs dates back to the early 1800s, with numerous inventors contributing to their development, culminating in Thomas Edison's patent for an improved incandescent bulb in 1879. Incandescent bulbs work through the principle of incandescence, where a tungsten filament heats up and emits light as electricity passes through it, although a significant portion of energy is wasted as heat. In contrast, compact fluorescent bulbs utilize mercury vapor to generate light with less heat emission, producing a different light spectrum that can resemble natural daylight.
Light bulbs are typically rated by their electrical power consumption, with common household sizes ranging from 15 to 150 watts in the U.S. Efficiency is further evaluated through luminous efficacy, which measures how effectively a bulb converts electricity into visible light. The cultural impact of light bulbs is also notable, as they are often referenced in humor and jokes, highlighting their ubiquitous presence in daily life. Overall, light bulb design plays a crucial role in both practical lighting solutions and broader cultural expressions.
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Light bulb design
Summary: Light bulbs are ideally designed for great luminous efficacy, emitting more light than heat.
Light bulbs are common sources of electric lighting. The light bulb’s evolution is not entirely certain. Historians cite more than 20 contributors, dating back to roughly 1800, who made discoveries prior to inventor Thomas Edison’s 1879 patent for an incandescent bulb. Some attribute Edison’s success to the fact that he also invented an entire electricity distribution system.
Traditionally, light bulbs work on the principle of incandescence. The filament inside an incandescent bulb resists the flow of electrons supplied by an electrical source, causing the filament to heat up and emit radiation. Approximately 90% of the power consumed by an incandescent light bulb is, in fact, emitted as heat rather than as visible light. The wavelength of the emitted radiation determines the color of the light. In common household incandescent bulbs, the emitted radiation is primarily in the infrared region of the spectrum, which humans cannot see, along with the visible red, orange, and yellow wavelengths nearest the infrared. This characteristic gives the bulb its characteristic yellowish color.
Compact fluorescent light bulbs, which are intended to replace incandescent bulbs, operate on a different principle. Electricity excites mercury vapor to produce light, but little heat. The emitted spectrum of traditional fluorescents is much closer to the blue end of the visible spectrum, though there are now a variety of models that closely mimic natural light. In addition to quantifying the emitted radiation spectrum, mathematics is used to calculate other important features of light bulbs, such as electrical rating and efficiency.
Rating
Incandescent bulbs are normally rated according to their electrical power. Common household sizes in the United States range from 15 watts, often found in refrigerators and other appliances, to 150-watt bulbs used for reading or to light large areas. As the bulb is purely resistive (its inductance and capacitance are insignificant), the electrical power can be computed as P=V×I, or P=I2×R, where P is the electric power in units of watts, V is the potential difference in volts, R is the resistance of the filament in ohms, and I is the current in amperes or “amps,” named after André-Marie Ampère, a French mathematician and physicist considered the “father of electrodynamics.” Household voltage in the United States is usually 120 volts, so higher wattage bulbs require more current to operate, which makes them more costly to use. Because compact fluorescents operate on a different principle than resistance, they typically draw less current to produce the same perceived intensity of light.
Luminous Efficacy
Another metric used to distinguish light bulbs is luminous efficacy, defined as
where F, the flux in lumens, is the total useful amount of visible radiant light, and P is the power. A weighted luminosity function adjusts for the human eye’s response to different wavelengths of light when flux is calculated. If total electric power consumed by a bulb is used in this computation, it is referred to as “luminous efficacy of a source” (LES). LES is a good indicator of source’s ability to provide visible light from a given amount of electricity. For example, a 40-watt incandescent bulb has an LES of roughly 12.6 lm/W, and a flux comparable to a 9- to 13-watt compact fluorescent. A 100-watt bulb has a flux comparable to 17.5 lm/W, versus a 23- to 30-watt compact fluorescent.
Humor
Light bulbs are also a source of humor, with hundreds of light bulb jokes of the general form, “How many (fill in the blank) does it take to screw in a light bulb?” Many of these jokes are intended to satirically poke fun at the subjects; mathematicians are no exception. For example, “How many mathematicians does it take to screw in a light bulb?” The answer is “None. A mathematician can’t screw in a light bulb, but he can easily prove the work can be done.”
Bibliography
Collier, James L. Electricity and the Light Bulb. Tarrytown, NY: Marshall Cavendish Benchmark, 2006.
Kaufman, John. IES Lighting Handbook 1981 Reference Volume. New York: Illuminating Engineering Society of North America, 1981.