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Types of Lighting

Incandescent Lamps

An incandescent lamp harnesses light from a heated material. Electric current flows through a thin tungsten wire (the filament) and heats the filament to about 3000°C, which causes heat and light to emit. The bulky globe or shell is under a vacuum, forming a heat insulator to keep the bulb and socket from getting too hot. The filament also produces infrared (heat) radiation, some of which is absorbed by the glass bulb wall as it passes, contributing more heat to the bulb. In addition, an inert gas is inside the bulb to prevent the filament from burning out.

Incandescent bulbs are now considered the least energy-efficient light source, but are still considered the traditional format of electric lighting. Incandescent bulbs dissipate a lot of the electricity they use as heat to accompany the light emitted from its glowing filament.

Facts about incandescent lamps:

• The rare gas krypton is mixed with the nitrogen and argon inside the glass bulb to allow the filament to operate at a higher temperature (and produce brighter light).
• The potential life is maximized to 1,000 hours of operation and 22 lumens of light output per watt.
• Lamps are available in compact fused-quartz glass tubes.
• They are relatively inexpensive ($.60 to $1), convenient to install, and readily available.
• 10% of its energy is emitted in the form of light.
• Incandescents have the highest color rendition index (CRI). The CRI measures how accurately a light source represents an object's color compared to an ideal source like the sun. Incandescents have a CRI of around 95.

Fluorescent Lamps

A fluorescent lamp is a low-pressure mercury vapor lamp confined in a glass tube, which is coated on the inside with a fluorescent material known as phosphor. The energized filament delivers electrons to the ionized inert gas within (usually argon), forming a plasma that conducts electricity. The ballast limits the flow of the current through the tube. Consequently, the plasma excites the mercury vapor atoms which then emits a spectra of red, green, blue, and ultraviolet lights. The internal phosphor coating then converts the ultraviolet light into other colors.

Facts about fluorescent lamps:

• The efficacy of the ultraviolet light transmission is dependent on the type of phosphor used.
• On average, 40 watts of energy in a fluorescent tube produces as much light as a 150-watt incandescent bulb.
• Compared to traditional incandescent bulbs, less heat is generated from the filament at similar lighting output.

Compact Fluorescent Lamps

The classic applications for compact fluorescents are outdoors lighting and security lighting where they run steadily for extended periods.

Facts about compact fluorescent lights:

• Frequent on/off switching noticeably affects its claimed life.
• They come in specialized designs and smaller sizes.
• Are compatible with existing screw sockets, hence relamping expenses are not an issue.
• Have an average life of roughly 10,000 hours.
• A 13-watt compact fluorescent lamp replaces a 60-watt incandescent with a ballast loss of about 2 watts.

Halogen Lamps

A halogen lamp is an incandescent bulb with a halogen gas added to reduce evaporation. Halogen lamps run at a higher temperature, providing a whiter light and greater efficiency. Widely used for display, accent lighting, halls, and lobbies, halogen lamps are used in many of the more modern lighting fixtures. Other types of popular halogen lamps are described below.

Low-pressure sodium—This light source converts nearly 35% of the energy consumed into light. Low-pressure sodium bulbs should last at least 10,000 hours and deliver as much light at the end of their life as in the beginning. However, they are the most expensive lighting source. They are also the largest, and hence, most difficult to control in terms of light distribution. In addition, because of their singular yellow color, they have very low color rendition index (CRI). Objects under low-pressure sodium illumination appear yellow, gray, or black.

High-intensity discharge (HID) lighting—These light sources are the elite, energy-efficient lighting devices on the market today for outdoor illumination. Each of these lamps requires a specially designed ballast and has a high initial cost. However, their lower operating cost rapidly returns the initial investment. High-intensity discharge lamps have one potential drawback that may limit their use — a start-up delay from 1 to 7 minutes from the time they are switched on until they fully illuminate. There are two particular types:

• Metal halide lamps—Metal halide lamps have the best CRI of the high-intensity discharge lamps. They are sometimes used for commercial interior lighting because of their excellent color and are the preferred light source for stadiums where there are television broadcasts. They are more efficient than mercury vapor lamps while having the same light output.
• High-pressure sodium lamps—High-pressure sodium lamps produce a golden white color that tends to blacken red and blue objects. Because their CRI is about 25, these lamps are rarely used for interior commercial lighting. They are used more frequently for interior industrial applications, such as in warehouses and manufacturing. Their small size and excellent efficiency make them the most popular choice for street and area lighting.