Incandescent Lamps
The original bulb used a carbon filament in a bulb containing a vacuum. Modern bulbs now primarily use tungsten filaments with a gas fill instead of a vacuum, though bulbs using thin filaments and lower currents still utilize a vacuum because they function more efficiently.
The filament acts as a resistor. An electric current passes through the filament, and resistance in the filament causes it to heat and incandesce. Filaments typically reach temperatures well over 2000 degrees Celsius. Most of the energy consumed by the bulb is given off as heat, causing its Lumens per Watt (LPW) performance to be low. Because of the filament's high temperature, the tungsten tends to evaporate and collect on the sides of the bulb. The inherent imperfections in the filament causes it to become thinner unevenly. When a bulb is turned on, the sudden surge of energy can cause the filament to break, because the thin areas heat up so much faster than the rest of the filament, leading to bulb failure.
Incandescent lamps exhibit smooth, even spectral power distribution (SPD) because they use the heat of a solid object to produce light. Incandescent lamps also score very high on CRI ratings, but because standard incandescent lamps produce very little radiant energy in the short wavelength end of the spectrum, they do not render blues very well. The low color temperature combined with a high CRI casts a warm light which provides excellent color rendition of skin tones. In addition, incandescent lamps are affordable, can be controlled by dimming circuits, and are available in a wide range of sizes, configurations and wattages.
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| INCANDESCENT BULB TYPES |
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Compact Fluorescent Light & Linear Fluorescent Lamps
These lamps feature a narrow tube space (1/2 to 5/8 in diameter) that is doubled back on itself and terminated in a plastic base. Compact fluorescent lamps are small enough to replace incandescent lamps in diffuse source applications and therefore bring the increased efficiency of fluorescent technology to a much larger variety of fixtures. Lamps with an internal ballast can be used in a typical incandescent socket. Other lamps use an external magnetic or electronic ballast. A fluorescent lamp is a gaseous discharge light source. Light is produced by passing an electric arc between tungsten cathodes in a tube filled with a low pressure mercury vapor and other gases. The arc excites the mercury vapor which generates radiant energy, primarily in the ultraviolet range. This energy causes the phosphor coating on the inside of the tube to fluoresce, converting the ultraviolet into visible light.
To start the lamp, a high voltage surge is needed to establish an arc in the mercury vapor. Once the lamp is started, the gas offers a decreasing amount of resistance, which means that the current must be regulated to match this drop. Without regulation, the lamp would draw power unceasingly and would rapidly burn out. By using a ballast the starting voltage is provided and the subsequent flow of current to the lamp is controlled. Using a balanced lamp/ballast system extends lamp life, increases energy efficiency, improves color characteristics, and enhances luminous efficacy.
Fluorescent lamps offer more color options than any other lamp type. This is due to the phosphor coating on the inside of the tube. Halophosphor is the basic coating. Along with rare earth and triphosphor coatings a control over the generation of red, green and blue is achieved. This has enabled the development of high lumens per watt (LPW) lamps in a variety of color temperatures that feature excellent color quality and provide spectacular renditions of virtually all colors.
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| COMPACT FLUORESCENT BULBS |
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The Halogen bulb (cycle)
The halogen cycle describes a complex chemical interaction between tungsten, oxygen and a halide that makes tungsten halogen lamps possible. Incandescent lamps operate by using an electric current to heat a filament so that it glows. The material that evaporates from the hot filament builds up on the inner bulb-wall and darkens the lamp. This "lamp blackening" becomes even more severe when the filament is situated near the bulb-wall, as in thin tubular lamps. The halogen cycle prevents lamp blackening and extends the service life of the bulb.
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| HALOGEN BULB TYPES |
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High Intensity Discharge Lighting
There are three primary types of HID lamps: metal halide, sodium, and mercury vapor. HID technology is very similar to fluorescent technology: an arc is established between two electrodes in a gas filled tube which causes a metallic vapor to produce radiant energy. The major difference is that HID lamps can produce visible light without any phosphors. In addition, the electrodes are only a few inches apart and the gases in the tube are highly pressurized. The arc acquires an extremely high temperature, causing metallic elements within the gas atmosphere to vaporize and release massive amounts of radiant energy.
A ballast is required in order to operate the HID lamp. Unlike fluorescent lamps, the ballast must be specifically designed for the lamp type and wattage being used. Also, the lamps require a warm-up period to achieve full light output, and in some cases require several minutes before they can be re-ignited after they are shut off.
Metal Halide
Metal Halide lamps offer high efficacy, excellent color rendition, long service life, and good lumen maintenance. They are used often in outdoor applications and in commercial interiors.
High pressure sodium lamps are very energy efficient. Mercury and sodium vapors produce a yellow/orange light with extremely good lumens per watt performance. Although they tend to render colors poorly they have an exceptionally long service life, (up to 40,000 hours).
Mercury vapor is the oldest HID technology. The light within the arc is bluish making it poor for rendering colors accurately. Because of this, a phosphor coating is sometimes applied to alter the color temperature and to improve color rendering.
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| HID BULB TYPES |
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