Energy Efficient Lighting
Summary: This section will provide you with information on how to save energy and reduce your costs when lighting your home. The quantity and quality of light around us determine how well we see, work, and play. Light affects our health, safety, morale, comfort, and productivity.
Lighting also directly affects our economy. As a nation, we spend about one-quarter of our electricity budget on lighting, or more than $37 billion annually. Yet much of this expense is unnecessary. Technologies developed during the past 10 years can help us cut lighting costs 30% to 60% while enhancing lighting quality and reducing environmental impacts.
- To save energy while maintaining good light quality and quantity, you need to understand:
Lighting principles and definitions
Types of lighting and how each works
Energy efficient lighting options, including daylighting, for new or retrofit applications.
Lighting Principles and Terms
To choose the best lighting options, you should understand basic lighting terms. This section explains terminology used in the industry, which will help you better understand the potentially confusing language you could hear in a lighting store.
Illumination: A lumen is a measurement of light output from a lamp, often called a tube or a bulb. All lamps are rated in lumens. For example, a 100-watt incandescent lamp produces about 1750 lumens.
The distribution of light on a horizontal surface is called its illumination. Illumination is measured in foot candles. A foot candle of illumination is a lumen of light distributed over a 1-square-foot (0.09-square-meter) area. The amount of illumination required varies according to the difficulty of a visual task. Ideal illumination is the minimum foot candles necessary to allow you to perform a task comfortably and proficiently without eyestrain. The Illuminating Engineering Society says that illumination of 30 to 50 foot candles is adequate for most home and office work. Difficult and lengthy visual tasks-like sewing for extended periods of time-require 200 to 500 foot candles. Where no seeing tasks (i.e., tasks whose speed and accuracy of completion are affected by quality and quantity of light) are performed, lighting systems need to provide only security, safety, or visual comfort-requiring from 5 to 20 foot candles of illumination.
Another lighting term you will hear is efficacy. This is the ratio of light output from a lamp to the electric power it consumes and is measured in lumens per watt (LPW).
Lighting Uses: Experts divide lighting uses into three categories: ambient, task, and accent lighting. Ambient lighting provides security and safety, as well as general illumination for performing daily activities. The goal of task lighting is to provide enough illumination so that tasks can be completed accurately but not provide so much light that entire areas are illuminated. Accent lighting illuminates walls so they blend more closely with naturally bright areas like ceilings and windows.
Light Quality: Light quality describes how well people in a lighted space can see to do visual tasks and how visually comfortable they feel in that space. Light quality is important to energy efficiency because spaces with higher quality lighting need less illumination. High-quality lighting is fairly uniform in brightness and has no glare. For example, direct intense sunlight streaming through the windows of a room with chocolate brown carpets and dark wall paneling will likely give too much contrast in brightness. The pupils of your eyes will constantly adjust to the differing brightness. Making this area visually comfortable would involve using lots of artificial lighting with a high illumination level.
On the other hand, in a pale-colored room bathed in soft light, you can hardly tell where the light is coming from because no one area of the room appears much brighter than another. The walls, ceiling, floor, and work surfaces are relatively the same light hue. People can perform tasks faster and with fewer mistakes with this type of high-quality lighting. Also, lighting such a room requires far less artificial lighting than the previous example.
Glare: Eliminating glare (i.e., excessive brightness from a direct light source) is essential to achieving good lighting quality. Types of glare include direct glare, reflected glare, and veiling reflections. Direct glare results from strong light from windows or bright lamps shining directly into your eyes. Reflected glare is caused by strong light from windows or lamps that is reflected off a shiny surface into your eyes. Veiling reflection is a special type of reflected glare that can obscure contrasts and reduce task clarity. Veiling reflections occur when light is reflected into your eyes from a work surface, such as a printed page or a computer screen.
Light Color and Color Rendering: Lamps are assigned a color temperature (using the Kelvin temperature scale) based on their "coolness " or "warmness." The human eye perceives colors as cool if they are at the blue-green end of the color spectrum, and warm if they are at the red end of the spectrum. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Contrast is the brightness difference between different parts of the visual field, which is the expanse of space you can see at a given instant without moving your eyes. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing.
Keep in mind, though, that artificial light sources vary widely in their color rendering indexes (CRI). The CRI is a measurement of a light source's ability to render colors the same as sunlight does. For example, incandescent lamps are rated at a CRI of 100-nearly equal to sunlight-while some high-pressure sodium lamps have a CRI of 22, which means they render colors very poorly.
However, a light's color-rendering ability is not related to whether it is a cool or warm color. For example, blue light from the northern sky, white light at noon, and red light from a sunset all have perfect color rendering (a CRI of 100) because our eyes are designed to read the colors of objects illuminated by sunlight.
Types of Lighting: There are four basic types of lighting: incandescent, fluorescent, high-intensity discharge, and low-pressure sodium.
Incandescent lighting is the most common type of lighting used in residences. Fluorescent lighting is used primarily in commercial indoor lighting systems, while high-intensity discharge lighting is used only for outdoor lighting applications. Low-pressure sodium lighting is used where color rendering is not important, such as highway and security lighting. These lighting types vary widely in their construction, efficiency, color characteristics, and lamp life.
Incandescent: Incandescent lamps are the least expensive to buy but the most expensive to operate. Incandescent light is produced by a tiny coil of tungsten wire that glows when it is heated by an electrical current. Incandescent lamps have the shortest lives of the common lighting types. They are also relatively inefficient compared with other lighting types. However, significant energy and cost savings are possible if you select the right incandescent lamp for the right job. The three most common types of incandescent lights are standard incandescent, tungsten halogen, and reflector lamps.
Standard incandescent: Known as the "A-type light bulb, " these lamps are the most common yet the most inefficient light source available. Larger wattage bulbs have a higher efficacy than smaller wattage bulbs. Note that 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 long-life bulbs last longer than their regular counterparts, they are less energy efficient.
Tungsten halogen: This newer type of incandescent lighting achieves better energy efficiency than the standard A-type bulb. It has 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 are considerably more expensive than standard incandescents and are primarily used in commercial applications: theater, store, and outdoor lighting systems.
Reflector lamps: Reflector lamps (Type R) are designed to spread light over specific areas. They are used mainly indoors for stage/theater and store applications, as well as floodlighting, spotlighting, and down lighting.
Parabolic aluminized reflectors (Type PAR) are used for outdoor floodlighting. The ellipsoidal reflector (Type ER) focuses the light beam about 2 inches (5 centimeters) in front of its enclosure and is designed to project light down from recessed fixtures. Ellipsoidal reflectors are twice as energy efficient as parabolic reflectors for recessed fixtures.
Fluorescent: The light produced by a fluorescent tube is caused by an electric current conducted through mercury and inert gases. Fluorescent lighting is used mainly indoors-both for ambient and task lighting-and is about 3 to 4 times as efficient as incandescent lighting. Fluorescent lamps last about 10 times longer than incandescents. But, to gain the most efficiency, you should install fluorescents in places where they will be on for several hours at a time.
Fluorescent lights need ballasts (i.e., devices that control the electricity used by the unit) for starting and circuit protection. Ballasts consume energy. You can increase the energy savings for existing fluorescent lighting by relamping (e.g., replacing an existing lamp with one of a lower wattage), replacing ballasts, and replacing fixtures with more efficient models.
Tube fluorescent: These lamps are the next most popular lamps after A-type incandescent lamps. 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 because their low brightness creates less direct glare than do incandescent bulbs.
Compact fluorescent: Compact fluorescent lamps (CFLs) are the most significant lighting advance developed for homes in recent years. They combine the efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures. CFLs can replace incandescents that are roughly 3 to 4 times their wattage, saving up to 75% of the initial lighting energy. Although CFLs cost from 10 to 20 times more than comparable incandescent bulbs, they last 10 to 15 times as long. This energy savings and superior longevity make
CFLs are one of the best energy efficiency investments available. When introduced in the early- to mid-1980s, CFLs were bulky, heavy, and too big for many incandescent fixtures. However, newer models with lighter electronic ballasts are only slightly larger than the incandescent lamps they replace.
CFLs come in integral and modular designs. Integral CFLs have a ballast and a lamp in a single disposable unit. Modular designs feature a separate ballast that serves about five lamp replacements before it wears out.
Figure 108: Energy Star-compliant compact fluorescent light bulbs.