Types of Lighting

You'll find that you have several options to consider when selecting what type of lighting you should use in your home.

When selecting energy-efficient lighting, it's a good idea to understand basic lighting terms and principles. Also, it helps to explore your lighting options for indoors and/or outdoors if you haven't already. This will help narrow your selection.

You can use the chart below to compare the different types of lighting.

Lighting Comparison Chart

Fluorescent Lighting

Fluorescent lamps use 25%–35% of the energy used by incandescent lamps to provide the same amount of illumination (efficacy of 30–110 lumens per watt). They also last about 10 times longer (7,000–24,000 hours).

The light produced by a fluorescent tube is caused by an electric current conducted through mercury and inert gases. Fluorescent lamps require a ballast to regulate operating current and provide a high start-up voltage. Electronic ballasts outperform standard and improved electromagnetic ballasts by operating at a very high frequency that eliminates flicker and noise. Electronic ballasts also are more energy-efficient. Special ballasts are needed to allow dimming of fluorescent lamps.

Improvements in technology have resulted in fluorescent lamps with color temperature and color rendition that are comparable to incandescent lamps.

Types of Fluorescent Lamps

Two general types of fluorescent lamps include these:

• Compact fluorescent lamps (CFLs)
• Fluorescent tube and circline lamps

You can use the chart below to compare these types of lamps. If you don't already, it helps to understand basic lighting principles and terms before making comparisons.

Fluorescent Tube and Circline Lamps

Fluorescent tube lamps—the second most popular type of lamps—are more energy efficient than the more popular A-type standard incandescent lamps.

The traditional tube-type fluorescent lamps are usually identified as T12 or T8 (12/8 or 8/8 of an inch tube diameter, respectively). They are installed in a dedicated fixture with a built-in ballast. The two most common types are 40-watt, 4-foot (1.2-meter) lamps, and 75-watt, 8-foot (2.4-meter) lamps.

Tubular fluorescent fixtures and lamps are preferred for ambient lighting in large indoor areas. In these areas, their low brightness creates less direct glare than incandescent bulbs.

Circular, tube-type fluorescent lamps are called circline lamps. They are commonly used for portable task lighting.

Compact Fluorescent Lamps

Compact fluorescent lamps (CFLs) combine the energy efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures.

CFLs can replace incandescents that are roughly 3–4 times their wattage, saving up to 75% of the initial lighting energy. Although CFLs cost 3–10 times more than comparable incandescent bulbs, they last 6–15 times as long (6,000–15,000 hours). See How CFLs Compare with Incandescents for more information.

How They Work

CFLs work much like standard fluorescent lamps. They consist of two parts: a gas-filled tube, and a magnetic or electronic ballast. The gas in the tube glows with ultraviolet light when electricity from the ballast flows through it. This in turn excites a white phosphor coating on the inside of the tube, which emits visible light throughout the surface of the tube.

CFLs with magnetic ballasts flicker slightly when they start. They are also heavier than those with electronic ballasts. This may make them too heavy for some light fixtures. Electronic ballasts are more expensive, but light immediately (especially at low temperatures). They are also more efficient than magnetic ballasts. The tubes will last about 10,000 hours and the ballast about 50,000 hours. Most currently available CFLs have electronic ballasts.

CFLs are designed to operate within a specific temperature range. Temperatures below the range cause reduced output. Most are for indoor use, but there are models available for outdoor use. You can find a CFL's temperature range on most lamp packages. You should install outdoor CFLs in enclosed fixtures to minimize the adverse effects of colder temperatures.

CFLs are most cost effective and efficient in areas where lights are on for long periods of time. You'll experience a slower payback in areas where lights are turned on for short periods of time, such as in closets and pantries. Because CFLs do not need to be changed often, they are ideal for hard-to-reach areas.

Types of Compact Fluorescent Lamps

CFLs are available in a variety of styles or shapes. Some have two, four, or six tubes. Others have circular or spiral-shaped tubes. The size or total surface area of the tube(s) determines how much light it produces.

Some CFLs have the tubes and ballast permanently connected. Other CFLs have separate tubes and ballasts. This allows you to change the tubes without changing the ballast. There are also types enclosed in a glass globe. These look somewhat similar to conventional incandescent light bulbs, except they're larger.

Sub-CFLs fit most fixtures designed for incandescent lamps. Although most CFLs fit into existing 3-way light sockets, only a few special CFL models can be dimmed.

High-Intensity Discharge Lighting

High-intensity discharge (HID) lamps provide the highest efficacy and longest service life of any lighting type. They can save 75%–90% of lighting energy when they replace incandescent lamps.

HID lamps use an electric arc to produce intense light. Like fluorescent lamps, they require ballasts. They also take up to ten minutes to produce light when first turned on, because the ballast needs time to establish the electric arc.

Because of the intense light they produce at a high efficacy, HID lamps are commonly used for outdoor lighting and in large indoor arenas. Since the lamps take awhile to establish, they are most suitable for applications where they stay on for hours at a time. They are not suitable for use with motion detectors.

Types of High-Intensity Discharge Lamps

These are the three most common types of HID lamps:

• Mercury vapor lamps
• Metal halide lamps
• High-pressure sodium lamps.

You can use the chart below to compare these types of lamps. If you don't already, it helps to understand basic lighting principles and terms before making comparisons.

Mercury Vapor Lamps

Mercury vapor lamps—the oldest types of high-intensity discharge lighting—are used primarily for street lighting.

Mercury vapor lamps provide about 50 lumens per watt. They cast a very cool blue/green white light. Most indoor mercury vapor lamps in arenas and gymnasiums have been replaced by metal halide lamps. Metal halide lamps have better color rendering> and a higher efficacy. However, like high-pressure sodium lamps, mercury vapor lamps have longer lifetimes (16,000–24,000 hours) than metal halide lamps.

Significant energy savings are also possible by replacing old mercury vapor lamps with newer high-pressure sodium lamps.

Metal Halide Lamps

Metal halide lamps produce a bright, white light with the best color rendition among high-intensity lighting types. They are used to light large indoor areas, such as gymnasiums and sports arenas, and outdoor areas, such as car lots.

Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamp results in higher light output, more lumens per watt, and better color rendition than from mercury gas alone.

Metal halide lamps have shorter lifetimes (5,000–20,000 hours) compared to both mercury vapor and high-pressure sodium lamps.

High-Pressure Sodium Lamps

High-pressure sodium lighting—a type of high-intensity discharge lighting—is becoming the most common type of outdoor lighting.

High-pressure sodium lamps have an efficacy of 50–140 lumens per watt—an efficiency exceeded only by low-pressure sodium lamps. They produce a warm white light. Like mercury vapor lamps, high-pressure sodium lamps have poorer color rendition than metal halide lamps but longer lifetimes (16,000–24,000 hours).

Incandescent Lighting

Incandescent lighting is the most common type of lighting used in homes. It has traditionally delivered about 85% of household illumination.

Incandescent lamps operate without a ballast. They light up instantly, providing a warm light and excellent color rendition. You can also dim them. However, incandescent lamps have a low efficacy compared to other lighting options (10–17 lumens per watt) and a short average operating life (750–2500 hours).

Incandescent lamps are the least expensive to buy, but because of their relative inefficiency and short life spans, they usually are more expensive to operate.

Types of Incandescent Lamps

These are the three most common types of incandescent lamps:

• Standard incandescent lamps
• Tungsten halogen lamps
• Reflector lamps

You can use the chart below to compare these types of lamps. If you don't already, it helps to understand basic lighting principles and terms before making comparisons.

Standard Incandescent Lamps

Known as the screw-in "A"-type light bulb, standard incandescent lamps are the most common—but the most inefficient—light source available.

These standard incandescent lamps produce light from a tiny coil of tungsten wire that glows when it is heated by an electrical current.

Larger wattage incandescent bulbs have a higher efficacy than smaller wattage bulbs. However, a larger wattage lamp or bulb may not be the most energy- or cost-effective option, depending on how much light is needed.

"Long-life" bulbs, with thicker filaments, are a variation of these A-type bulbs. Although these bulbs last longer than their counterparts, they are less energy efficient.

Tungsten Halogen Lamps

Tungsten halogen lamps—a type of incandescent lighting—achieve better energy efficiency than standard, incandescent A-type light bulbs.

Tungsten halogen lamps have a gas filling and an inner coating that reflect heat. Together, the filling and coating recycle heat to keep the filament hot with less electricity.

These lamps provide excellent color rendition. They also are considerably more expensive to buy than standard incandescent lamps, but are less expensive to operate because of their higher efficacy.

Reflector Lamps

Reflector lamps (Type R)—a type of incandescent lighting—spread and direct light over specific areas. They are used mainly for floodlighting, spotlighting, and downlighting.

There are two types of reflector lamps: parabolic aluminized and ellipsoidal. Parabolic aluminized reflector lamps (Type PAR) are used for outdoor floodlighting. Ellipsoidal reflector lamps (Type ER) focus light beams about 2 inches (5 centimeters) in front of its enclosure, projecting light down from recessed fixtures. Ellipsoidal reflectors are twice as energy efficient as parabolic reflectors for recessed fixtures.

Low-Pressure Sodium Lighting

Low-pressure sodium lamps provide the most energy-efficient outdoor lighting compared to high-intensity discharge lighting, but they have very poor color rendition. Typical applications include highway and security lighting, where color isn't important.

Low-pressure sodium lamps work somewhat like fluorescent lamps. Like high-intensity discharge lighting, low-pressure sodium lamps require up to ten minutes to start and have to cool before they can restart. Therefore, they are most suitable for applications where they stay on for hours at a time. They are not suitable for use with motion detectors.

You can use the chart below to compare low-pressure sodium lamps with high-intensity discharge lamps. If you don't already, it helps to understand basic lighting principles and terms before making comparisons.

Outdoor Solar Lighting

Outdoor solar lights are easy to install and virtually maintenance free. Best of all, they provide free electricity.

Outdoor solar lighting systems use solar cells, which convert sunlight into electricity. The electricity is stored in batteries for use at night. Manufacturers most commonly use nickel cadmium, sealed lead acid, and lead acid batteries.

Outdoor solar lighting systems will work in most areas of the United States. However, it is important to consider geographic and site specific variables when choosing a product. A solar lighting system will work well only as long as the solar cells receive the manufacturer's recommended hours of sunlight.

The "nightly run time" listings on most "off-the-shelf" products are based on specific sunlight conditions. Outdoor solar lights located in places that receive less sunlight than the solar cells need will operate for fewer hours per night than expected. Nightly run times may also vary depending on how clear the sky is on any given day. Operating times in the winter months may vary as much as 30%–50%. Unless the solar lighting system has been sized specifically for winter operation, it will not operate for the specified number of hours per night in a given location. Shading of the solar cells by landscape features (vegetation, buildings, etc) will also impact battery charging and performance. Watch for bird droppings, too. Insufficient battery charging will not only affect performance, it also may reduce the life of the battery.

Some solar lighting systems are self-contained units. You only need to place the lights in a sunny location. Others have the lights separate from a solar cell panel. Only the panel needs to be placed in a sunny location. Units vary in size from small eight-inch, red-glowing pathway markers to pole-mounted patio and high-beam security lights.

Before you buy an outdoor solar lighting system, check with the manufacturer to see if replacement bulbs or batteries are available. Some units do not provide replacement options.

Home outdoor solar lighting systems are often available in hardware, lighting, and discount stores as well as through environmentally oriented mail order companies.

Types of Solar Cells

The performance of a solar or photovoltaic (PV) cell is measured in terms of its efficiency at converting sunlight into electricity. There are a variety of solar cell materials available, which vary in conversion efficiency.

Semiconductor Materials

A solar cell consists of semiconductor materials. Silicon remains the most popular material for solar cells, including these types:

• Monocrystalline or single crystal silicon
• Multicrystalline silicon
• Polycrystalline silicon
• Amorphous silicon

The absorption coefficient of a material indicates how far light with a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed.

The bandgap of a semiconductor material is an amount of energy. Specifically, the bandgap is the minimum energy needed to move an electron from its bound state within an atom to a free state. This free state is where the electron can be involved in conduction. The lower energy level of a semiconductor is called the "valence band." The higher energy level where an electron is free to roam is called the "conduction band." The bandgap (often symbolized by Eg) is the energy difference between the conduction band and valence band.

Solar cell material has an abrupt edge in its absorption coefficient; because light with energy below the material's bandgap cannot free an electron, it isn't absorbed.

Thin Film

Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Thin film technology has made it possible for solar cells to now double as these materials:

• Rooftop or solar shingles
• Roof tiles
• Building facades
• Glazing for skylights or atria.

Thin-film rooftop or solar shingles, made with various non-crystalline materials, are just now starting to enter the residential market. The following are benefits of these solar shingles:

• Attractive integration into homes
• Dual purpose—serves as both roofing material and pollution-free electricity producer
• Durability.

Current issues with commercially-available solar shingles include their lower efficiencies and greater expense compared with the standard small solar electric system.

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Source: U.S. Dept. of Energy