The oldest type of electric lamp is the incandescent bulb, the first practical one having been created in 1879 by Thomas Edison. With the construction of electric-generating stations, incandescent lamps soon became commonplace. Today, they remain the most popular kind of lamp used in American homes.
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By definition, an incandescent lamp is a clear or frosted glass bulb having a looped filament and a metal screw base. Inside the bulb, the air (with its relatively high level of oxygen) has been removed so that combustion can’t occur. Generally, an inert gas (from a combustion standpoint) such as nitrogen, or a mixture of inert gases, is then pumped in at about a third of the normal atmospheric pressure. These inert gases are added to slow down the filament’s sublimation (a change of state from a solid directly to a gas). Sublimation results in the black discoloration seen in older bulbs.
When too much of a filament has sublimated, the bulb will burn out. Because of the inevitable process of sublimation, typical incandescent lamps generally don’t last as long as typical fluorescent lamps.
In many incandescent bulbs, the looped filaments are made of tungsten, a rare metallic element. When an incandescent bulb is turned on, the electric current enters through the metal screw base and flows into the tungsten filament. The filament temperature rises rapidly, up to several thousand degrees Fahrenheit. This causes the tungsten to glow. In reality, several forms of radiation are A large percentage of the electricity used by typical incandescent bulbs goes not to producing light but to generating unwanted heat.emitted. These include visible light, some ultraviolet rays and a great deal of infrared radiation (heat). In fact, a large percentage of the electricity used by typical incandescent bulbs goes, not to producing light, but to generating unwanted heat.
Traditionally, incandescent bulbs have been chosen over other lamp types for most residential applications: table and floor lamps as well as bedroom, hall and bath ceiling fixtures. This is because incandescent bulbs can be manufactured at low cost, in virtually any size or shape to fit nearly all types and sizes of fixtures. Also, their yellowish-white glow is considered by many to be warm and friendly.
Long-Life Bulbs
Incandescent lamps are now available that are designed for longer life or to emit a full spectrum that mimics natural-light.One interesting innovation that began a decade or so ago was the use of special diodes that were attached to the tips of the metal screw bases of certain incandescent bulbs. Diodes are tiny electronic devices that only permit electric current to pass through them in one direction. Home electric lines carry alternating current (AC) in which the flow of electricity repeatedly switches directions 60 times a second. Because a diode-equipped bulb uses only electricity flowing in one direction, it is only on half the time. This creates a continuous on/off light pattern, but it’s so rapid that most people can’t perceive it, so they just see continuous light. Because the bulb is on only half the time, the bulb’s life expectancy can be greatly extended. Bulbs with this particular adaptation are now not as commonly encountered as they once were.
Other developments to make bulbs last longer are the use of solid-brass screw bases, supports for the tungsten filament and the use of krypton gas to slow down the sublimation rate. It seems that krypton causes tungsten atoms to “bounce back” onto the filament. These days, most bulbs with “long life” on their labels use at least one of these approaches.
Halogen Bulbs
One major development was the introduction of halogen bulbs. Originally invented by General Electric in 1957, these are a bulb inside a bulb. The innermost bulb, filled with bromine and iodine under pressure, contains a tungsten filament. These halogen gases (a class of elements in which bromine and iodine belong) cause the tungsten molecules that are normally lost through sublimation to simply redeposit themselves on the filament. At the same time, the tungsten is able to burn more intensely. Surrounding this inner pressurized bulb is an outer protective bulb.
Halogen bulbs burn intensely, giving off a whiter light than typical incandescent bulbs, so there are more lumens (a measurement for the flow of light) per watt. These bulbs are also longer lasting — usually being rated for 2,000 to 3,000 hours of use. Another plus is their ability to create a more focused light source.
However, there are problems with halogen bulbs. A major one is the tremendous amount of heat that they produce. In fact, an amazing 90% of the energy created by halogen bulbs is in the form of infrared radiation (heat). As a result, some bulb temperatures reach as much as 1230° F. Therefore, halogen bulbs must be used only in fixtures designed for them.
By the way, not long ago halogen torchiers (floor lamps with reflector bowls and no shades designed to cast light upwards) became a hot news item. Apparently, people were placing them too near fabric curtains, which caught on fire. This is not surprising when you realize that these lamps operate at temperatures high enough to instantly cause paper and most fabrics to ignite. Now, newly manufactured halogen torchiers have protective grills above their reflector pans to help prevent accidental fires. However, it’s still a good idea to keep any halogen torchier at least several feet from any curtain or drapery. As a precaution, it may be a good idea, if you have a pet or small child that might accidentally knock a halogen torchier over, to remove it from your home and find another lighting option.
Another problem is the risk of the bulbs exploding. A warning in a GE Lighting catalog notes that halogen lamps, which are “constructed of a glass bulb with a pressurized internal filament tube that operates at high temperatures, could unexpectedly shatter. Should the outer bulb break, particles of extremely hot glass could be discharged into the fixture enclosure and/or surrounding environment, thereby creating a risk of personal injury or fire.” Apparently, however, this is a fairly uncommon scenario.
If you’re interested in halogen bulbs, again, make absolutely sure your fixtures are designed for them. It should be mentioned that cooler and shatter-resistant halogen bulbs are available.
Color-Corrected (Full Spectrum) Bulbs
An incandescent innovation is the color-corrected bulb. Lamps of this type are designed to closely mimic the spectrum of natural sunlight, rather than the yellowish glow of typical incandescent bulbs. Some people feel that humans derive a health benefit from exposure to light indoors that is similar to sunlight. This health benefit has not held up to current research. However, full-spectrum lamps can make colors seem more natural indoors.
From Creating a Healthy Household: The Ultimate Guide For Healthier, Safer, Less-Toxic Living, © 2000 by Lynn Marie Bower.
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