BIRDS & LIGHTING - Incandescent Light #1
BIRDS & LIGHTING - Incandescent Light #1Incandescent Light Principles
Although forms of the incandescent light had been experimented with since the 1840's, Thomas Edison’s development of a bulb which incorporated a carbon filament of bamboo became the first to be practical application of electrical lighting. As we well know, the electric lamp has forever changed our patterns in the world, allowing for the first time complete mastery over daylight and darkness. These first devices were fragile to use, and in 1907, the more mechanically stable metallic element tungsten was substituted for the carbonized filaments of the Edison lamp. The light bulb as we know it
became a reality in 1913, when the “Mazda” bulb introduced inert gasses into the glass envelope to prolong the life of the filament. Figure 1 shows the structure of a conventional incandescent lamp:
FIGURE 1 - THE INCANDESCENT LAMP
The operational principles of the incandescent lamp are quite simple. I quote the following explanation of how it functions:
“If an electric current is passed through any conductor other than a perfect one (Editor’s note: such as gold at cryogenic temperatures), a certain amount of energy is expended that appears as heat in the conductor. Inasmuch as any heated body will give off a certain amount of light at temperatures over 525o C (977o F), a conductor heated above that temperature by an electric current will act as a light source. The incandescent lamp consists of a filament of a material with a high melting point sealed inside a glass bulb from which the air has been evacuated, or which is filled with an inert gas. Filaments with high melting points must be used, because the proportion of light energy to heat energy radiated by the filament rises as the temperature increases, and the most efficient light source is obtained at the highest filament temperature. Carbon filamentsScrew type bulb devices which use the incandescent principle (see also: Black Body Radiation) typically radiate the greatest amount of their energy within the infrared spectrum. A common tungsten filament operates at 2685o C (4868o F), well below its melting point. At these temperatures, the peak output is approximately 10,000 Angstroms (1000 nanometers), and falls in a linear manner through the visible spectrum to approximately 3500 nanometers, or about the center of the Near (UVA) range. Thus, the majority of the output of the conventional incandescent lamp is in the lower, yellow to red segment of the visible spectrum. For an assessment of the lighting perspectives of these and other incandescent devices, please see Incandescent Lights.
were employed in the first practical incandescent lamps, but modern lamps are universally made with filaments of fine tungsten wire, which has a melting point of 3410o C (6170o F). The filament must be enclosed in either a vacuum or an inert atmosphere, otherwise the heated filament would react chemically with the surrounding atmosphere.Using an inert gas instead of a vacuum in incandescent lamps has the advantage of slowing evaporation of the filament, thus prolonging the life of the lamp. Most modern incandescent lamps are filled with a mixture of argon and halogen gases or a small amount of nitrogen or krypton. Radical changes in incandescent lamp design have resulted from substituting compact fused-quartz glass tubes for glass bulbs.” ("Electric Lighting," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft Corporation.
Copyright (c) 1994 Funk & Wagnall's Corporation.)
Copyright 1999 by Patrick Thrush
