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A Consumer's Guide to Energy Efficiency and Renewable Energy Lighting
Artificial lighting consumes almost 15% of a household's electricity use. Use of new lighting technologies can reduce lighting energy use in homes by 50%–75%.
You can reduce lighting energy use by selecting lighting and sources that use energy more efficiently, and by installing lighting controls.
Here you'll find the following information:
Reading List
Efficient Lighting Strategies (PDF 691 KB). |
Lighting Principles and Terms
To choose the best energy-efficient lighting options for your home, you should understand basic lighting principles and terms.
Light Quantity
Illumination—The distribution of light on a horizontal surface. The purpose of all lighting is to produce illumination.
Lumen—A measurement of light emitted by a lamp. As reference, a 100-watt incandescent lamp emits about 1750 lumens.
Footcandle—A measurement of the intensity of illumination. A footcandle is the illumination produced by one lumen distributed over a 1-square-foot area. For most home and office work, 30–50 footcandles of illumination is sufficient. For detailed work, 200 footcandles of illumination or more allows more accuracy and less eyestrain. For simply finding one's way around at night, 5–20 footcandles may be sufficient.
Energy Consumption
Efficacy—The ratio of light produced to energy consumed. It's measured as the number of lumens produced divided by the rate of electricity consumption (lumens per watt).
Light Quality
Color temperature—The color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2700–3600 K is generally recommended for most indoor general and task lighting applications.
Color rendition—How colors appear when illuminated by a light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendition Index (CRI) is a 1–100 scale that measures a light source's ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb. A light source with a CRI of 80 or higher is considered acceptable for most indoor residential applications.
Glare—The excessive brightness from a direct light source that makes it difficult to see what one wishes to see. A bright object in front of a dark background usually will cause glare. Bright lights reflecting off a television or computer screen or even a printed page produces glare. Intense light sources—such as bright incandescent lamps—are likely to produce more direct glare than large fluorescent lamps. However, glare is primarily the result of relative placement of light sources and the objects being viewed.
Lighting Uses
Ambient lighting—Provides general illumination indoors for daily activities, and outdoors for safety and security.
Task lighting—Facilitates particular tasks that require more light than is needed for general illumination, such as under-counter kitchen lights, table lamps, or bathroom mirror lights.
Accent lighting—Draws attention to special features or enhances the aesthetic qualities of an indoor or outdoor environment.
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Indoor and Out Door Lighting Design
Energy-efficient lighting design focuses on ways to improve both the quality and efficiency of lighting.
Here you'll find basic information about energy-efficient lighting design principles and methods for the following:
If you're constructing a new house, you want to consider lighting as part of your whole-house design—an approach for building an energy-efficient home.
Indoor Lighting Design
When designing indoor lighting for energy efficiency, you want to consider some basic design principles and methods.
Energy-efficient lighting design principles include the following:
- Remember that more light is not necessarily better. Human visual performance depends on light quality as well as quantity.
- Match the amount and quality of light to the performed function.
- Install task lights where needed and reduce ambient light elsewhere.
- Use energy-efficient lighting components, controls, and systems.
- Maximize the use of daylighting.
Here are some basic methods for achieving energy-efficient indoor lighting:
- Install fluorescent light fixtures for all ceiling- and wall-mounted fixtures that will be on for more than 2 hours each day. These often include the fixtures in the kitchen and living room, and sometimes those in bathrooms, halls, bedrooms, and other higher-demand locations.
- Install dedicated compact fluorescent fixtures, rather than compact fluorescent lamps (CFLs) in incandescent fixtures, so that fluorescent bulbs continue to be used for the life of the house.
- Use CFLs in portable lighting fixtures that are operated for more than 2 hours a day.
- Use ENERGY STAR labeled lighting fixtures.
- Use occupancy sensors for automatically turning on and off your lights as needed.
- Consider light wall colors to minimize the need for artificial lighting.
- If recessed lights are used in a ceiling with an unconditioned space above it, use only Underwriters Laboratory (UL) approved fixtures that are airtight, are IC (insulation contact) rated, and meet ASTM E283 requirements.
Outdoor Lighting Design
When designing outdoor lighting, you need to consider the purpose of the lighting along with the basic methods for achieving energy efficiency.
Outdoor lighting for homes generally serves one or a combination of three main purposes:
- Aesthetics
Illuminate the exterior of the house and landscape.
- Security
Illuminate the grounds near the house or driveway.
- Utility
Illuminate the porch and driveway to help people navigate safely to and from the house.
Here are some basic methods for achieving energy-efficient outdoor lighting:
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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.
Types of lighting include:
You can use the chart below to compare the different types of lighting.
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Lighting Comparison Chart |
|
Lighting Type |
Efficacy
(lumens/watt) |
Lifetime
(hours) |
Color Rendition Index (CRI) |
Color Temperature (K) |
Indoors/Outdoors |
|
|
|
Standard "A" bulb |
10–17 |
750–2500 |
98–100 (excellent) |
2700–2800 (warm) |
Indoors/outdoors |
|
Tungsten halogen |
12–22 |
2000–4000 |
98–100 (excellent) |
2900–3200 (warm to neutral) |
Indoors/outdoors |
|
Reflector |
12–19 |
2000–3000 |
98–100 (excellent) |
2800 (warm) |
Indoors/outdoors |
|
Fluorescent |
|
Straight tube |
30–110 |
7000–24,000 |
50–90 (fair to good) |
2700–6500 (warm to cold) |
Indoors/outdoors |
|
Compact fluorescent lamp (CFL) |
50–70 |
10,000 |
65–88 (good) |
2700–6500 (warm to cold) |
Indoors/outdoors |
|
Circline |
40–50 |
12,000 |
|
|
Indoors |
|
High-Intensity Discharge |
|
Mercury vapor |
25–60 |
16,000–24,000 |
50 (poor to fair) |
3200–7000 (warm to cold) |
Outdoors |
|
Metal halide |
70–115 |
5000–20,000 |
70 (fair) |
3700 (cold) |
Indoors/outdoors |
|
High-pressure sodium |
50–140 |
16,000–24,000 |
25 (poor) |
2100 (warm) |
Outdoors |
|
Low-Pressure Sodium |
60–150 |
12,000–18,000 |
-44 (very poor) |
|
Outdoors |
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Lighting Controls
Most everyone knows that you can save energy by turning off lights when they're not needed. But sometimes we forget or don't notice that we've left lights on. Lighting controls can be used to automatically turn lights on and off as needed, preventing energy waste.
The most common types of lighting controls include the following:
Before purchasing and using any lighting controls, 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.
Lighting Dimmer Controls
Dimmer controls provide variable indoor lighting for incandescent and fluorescent lamps. When you dim these lamps, it reduces their wattage and output, which helps save energy.
Off-the-shelf dimmers for incandescent fixtures are inexpensive and provide some energy savings when lights are used at a reduced level. Dimmers also increase the service life of incandescent lamps significantly. However, dimming incandescent lamps reduces their lumen output more than their wattage. This makes incandescent lamps less efficient as they are dimmed.
Dimming fluorescents requires special dimming ballasts and lamp holders, but does not reduce their efficiency. Fluorescent dimmers are dedicated fixtures and bulbs that provide even greater energy savings than a regular fluorescent lamp.
Lighting Motion Sensor Controls
Motion sensors automatically turn outdoor lights on when they are needed (when motion is detected) and turn them off a short while later. They are very useful for outdoor security and utility lighting provided by incandescent lamps.
Because utility lights and some security lights are needed only when it is dark and people are present, the best way to control might be a combination of motion sensor and photosensor.
Incandescent flood lights with a photosensor and motion sensor may actually use less energy than pole-mounted high-intensity discharge (HID) or low-pressure sodium security lights controlled by a photosensor. Even though HID and low-pressure sodium lights are more efficient than incandescents, they are turned on for a much longer period of time than incandescents using these dual controls.
When turned on, HID and low-pressure sodium lamps can also take up to ten minutes to produce light. Therefore, they don't work well with just a motion sensor.
Lighting Occupancy Sensor Controls
Occupancy sensors—indoor lighting controls—detect activity within a certain area. They provide convenience by turning lights on automatically when someone enters a room. They reduce lighting energy use by turning lights off soon after the last occupant has left the room.
Occupancy sensors must be located where they will detect occupants or occupant activity in all parts of the room. There are two types of occupancy sensors: ultrasonic and infrared. Ultrasonic sensors detect sound, while infrared sensors detect heat and motion. In addition to controlling ambient lighting in a room, they are useful for task lighting applications, such as over kitchen counters. In such applications, task lights are turned on by the motion of a person washing dishes, for instance, and automatically turn off a few minutes after the person stops.
Lighting Photosensor Controls
You can use photosensors to prevent outdoor lights from operating during daylight hours. This can help save energy because you don't have to remember to turn off your outdoor lights.
Photosensors sense ambient light conditions, making them useful for all types of outdoor lighting. They offer little utility in controlling lights inside the home because lighting needs vary with occupant activity rather than ambient lighting levels.
Lighting Timer Controls
Timers can be used to turn on and off outdoor and indoor lights at specific times.
Simple timers are not often used alone for outdoor lighting because the timer may have to be reset often with the seasonal variation in the length of night. However, they can be used effectively in combinations with other controls. For example, the best combination for aesthetic (decorative) lighting may be a photosensor that turns lights on in the evening and a timer that turns the lights off at a certain hour of the night (e.g., 11 P.M.).
For indoor lighting, timers are sometimes used to give unoccupied houses a lived in look. However, they are an ineffective control for an occupied home because they do not respond to changes in occupant behavior, like occupancy sensors.
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Lamp and Ballast Replacement for Energy Efficiency
Relamping means substituting one lamp for another to save energy. You can decide to make illumination higher or lower when relamping. Be sure that the new lamp's lumen output fits the tasks performed in the space and conforms to the fixture's specifications.
Matching replacement lamps to existing fixtures and ballasts can be tricky, especially with older fixtures. Buying new fixtures made for new lamps produces superior energy savings, reliability, and longevity compared with relamping.
For more information, see these resources:
Before replacing a lamp and/or ballast in a light fixture, it's a good idea to first understand basic lighting principles and terms. This understanding will help you make the most economical purchase.
Replacing Lamps in Incandescent Lighting Fixtures
You can reduce lighting costs by replacing lamps in or "relamping" your older indoor and outdoor incandescent lighting fixtures.
Many older indoor lighting fixtures trap a significant portion of light inside the fixture. Newer incandescent fixtures are designed to push all their light out into the room. Others use smaller tungsten halogen lamps. Advances in indoor fixture design include brighter reflectors and better reflecting geometry.
Many incandescent lamps also are mismatched to their tasks or application. Some have excessive wattages and therefore create unnecessarily high illumination. For example, some outdoor fixtures tend to disperse much of their light beyond the intended area, which causes light pollution. This can be corrected by using lamps with smaller wattage.
A-type light bulbs can often be replaced with improved lamp designs, such as reflectors or tungsten halogen lamps. For energy savings of 60%–75%, many incandescent lamps can be replaced by compact fluorescent lamps (CFLs). A standard 18-watt CFL replaces a 75-watt A-type lamp. CFLs are especially economical in spaces where lights are needed for longer periods of time.
CFLs are also packaged in the same glass reflector lamps as incandescent lamps. Use CFLs packaged as ellipsoidal reflectors (type-ER) in recessed fixtures. Use reflector (R) or parabolic reflector (PAR) CFLs for flood and spotlighting. Some CFL fixtures have built-in electronic ballasts and polished metal reflectors.
When used in recessed fixtures, standard A-type lamps and reflector lamps waste energy because their light gets trapped. To save energy, you could replace a 150-watt standard reflector with a 75-watt ellipsoidal reflector (ER). Remember, though, that ER lamps are less efficient at delivering light from shallow fixtures, so use reflectors or parabolic reflectors for these purposes.
Before replacing a lamp in a light fixture, it's a good idea to first understand basic lighting principles and terms, if you don't already. This understanding will help you make the most economical purchase.
Replacing Lamps and Ballasts in Fluorescent Lighting Fixtures
Although fluorescent lamps are generally energy efficient, there are new, even more efficient lamps that use better electrodes and coatings than do older fluorescent lamps. These lamps produce about the same lumen output with substantially lower wattage.
Common 40-watt and 75-watt lamps can be replaced with energy-saving lamps of 34 watts and 60 watts, respectively. Energy-saving lamps for less-common fluorescent fixtures are also available.
If you need to replace the ballasts in your fluorescent fixtures, consider using one of the improved varieties. These fluorescent ballasts, called improved electromagnetic ballasts and electronic ballasts, raise the efficiency of the fixture 12%–30%.
Newer electromagnetic ballasts reduce ballast losses, fixture temperature, and system wattage. Because they operate at cooler temperatures, they last longer than standard electromagnetic ballasts.
Electronic ballasts operate at a very high frequency that eliminates flickering and noise. They are even more efficient than improved electromagnetic ballasts. Some electronic ballasts even allow you to operate the fluorescent lamp on a dimmer switch, which usually is not recommended with most fluorescents.
Before replacing a lamp and/or ballast in a light fixture, it's a good idea to first understand basic lighting principles and terms, if you don't already. This understanding will help you make the most economical purchase.
Fluorescent Lamp Disposal
All fluorescent lights contain small amounts of mercury. Some compact fluorescent lamps with magnetic ballasts contain small amounts of short-lived radioactive material. Because of these hazardous materials, you should not toss burned-out lamps into the trash.
Find out if there is a recycling program for them in your community—they are becoming more common. You can also dispose of the lamps with other household hazardous wastes such as batteries, solvents, and paints at your community's designated drop-off point or during a designated day when you can put such materials with your curb-side trash pickup.
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Lighting Maintenance
Maintenance is vital to lighting efficiency. Light levels decrease over time because of aging lamps and dirt on fixtures, lamps, and room surfaces. Together, these factors can reduce total illumination by 50% or more, while lights continue drawing full power.
The following basic maintenance suggestions can help keep your lights operating at their optimum energy efficiency:
- Clean fixtures, lamps, and lenses every 6–24 months by wiping off the dust. However, never clean an incandescent bulb while it is turned on. The water's cooling effect will shatter the hot bulb.
- Replace lenses if they appear yellow.
- Consider group relamping. Common lamps, especially incandescent and fluorescent lamps, lose 20%–30% of their light output over their service life. Many lighting experts recommend replacing all the lamps in a lighting system at once. This saves labor, keeps illumination high, and avoids stressing any ballasts with dying lamps.
- Clean or repaint small rooms every year and larger rooms every 2–3 years. Dirt collects on surfaces, which reduces the amount of light they reflect.
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When to Turn Off Your Lights
The cost effectiveness of when to turn off lights depends on the type of lights and the price of electricity. The type of light is important for several reasons. All types of lights have a nominal or rated operating life, which is the total number of hours that they will provide a specified level or amount of light. However, the operating life of all types of light bulbs is affected by how many times they are turned on and off. The more often they are switched on and off, the lower their operating life. The exact number of hours that switching lights on and off reduces the total operating life depends on the type of light and how many times it is switched on and off.
Incandescent Lighting
Incandescent lights (or bulbs) should be turned off whenever they are not needed. Nearly all types of incandescent light bulbs are fairly inexpensive to produce and are relatively inefficient. Only about 10%–15% of the electricity that incandescent lights consume results in light—the rest is turned into heat. Turning the light(s) off will keep a room cooler, an extra benefit in the summer. Therefore, the value of the energy saved by not having the lights on will be far greater than the cost of having to replace the bulb.
Fluorescent Lighting
The cost effectiveness of turning fluorescent lights off to conserve energy is a bit more complicated. For most areas of the United States, a general rule-of-thumb for when to turn off a fluorescent light is if you leave a room for more than 15 minutes, it is probably more cost effective to turn the light off. Or in other words, if you leave the room for only up to 15 minutes, it will generally be more cost effective to leave the light(s) on. In areas where electric rates are high and/or during peak demand periods, this period may be as low as 5 minutes.
Fluorescent lights are more expensive to buy, and their operating life is more affected by the number of times they are switched on and off, relative to incandescent lights. Therefore, it is a cost trade-off between saving energy and money by turning a light off "frequently" and having to replace the bulbs "more" frequently. This is because the reduction in usable lamp life due to frequent on/off switching will probably be greater than the benefit of extending the useful life of the bulb from reduced use. By frequent we mean turning the light off and on many times during the day.
It is a popularly held belief that fluorescent lights use a "lot" of energy to get started, and thus it is better not to turn them off for "short" periods. There is an increase in power demand when a light is switched on, and the exact amount of this increase depends on the type of ballast and lamp. The ballast provides an initial high voltage for starting the lamp and regulates the lamp current during operation. There are three basic types of ballasts: magnetic (of which there are energy-efficient and not so energy-efficient types), cathode-disconnect, and electronic. All types can operate two or more lamps simultaneously. There are three main methods that are used in a lamp's ballast to start the lamp: preheat, rapid-start, and instant-start.
In any case, the relatively higher "inrush" current required lasts for half a cycle, or 1/120th of a second. The amount of electricity consumed to supply the inrush current is equal to a few seconds or less of normal light operation. Turning off fluorescent lights for more than 5 seconds will save more energy than will be consumed in turning them back on again. Therefore, the real issue is the value of the electricity saved by turning the light off relative to the cost of relamping a fixture. This in turn determines the shortest cost-effective period for turning off a fluorescent light.
The value of the energy saved by turning a fluorescent light (or array of lights) off depends on several factors. The price an electric utility charges its customers depends on the customer "classes," which are typically residential, commercial, and industrial. There can be different rate schedules within each class. Some utilities may charge different rates for electricity consumption during different times of the day. It generally costs more for utilities to generate power during certain periods of high demand or consumption, called peaks. Some utilities can charge commercial and industrial customers more per kilowatt-hour (kWh) during peak periods than for consumption off-peak. Some utilities may also charge a base rate for a certain level of consumption and higher rates for increasing blocks of consumption. Often a utility adds miscellaneous service charges, a base charge, and/or taxes per billing period that could be averaged per kWh consumed, if these are not already factored into the rate.
Energy Savings
To calculate the exact value of energy savings by turning a light off, you need to first determine how much energy the light(s) consume when on. Every bulb has a Watt rating printed on it. For example, if the rating is 40 watts, and the bulb is on for one hour, it will consume 0.04 kWh, or if it is off for one hour, you will be saving 0.04 kWh. (Note that many fluorescent fixtures have two or more bulbs. Also, one switch may control several fixtures—an "array." Add the savings for each fixture to determine the total energy savings.)
Then you need to find out what you are paying for electricity per kWh (in general and during peak periods). You will need to look over your electricity bills and see what the utility charges per kWh. Multiply the rate per kWh by the amount of electricity saved, and this will give you the value of the savings. Continuing with the example above, let us say that your electric rate is 10 cents per kWh. The value of the energy savings would then be 0.4 cents ($ 0.004). The value of the savings will increase the higher the watt rating of the bulb, the greater the number of bulbs controlled by a single switch, and the higher the rate per kWh.
The most cost-effective length of time that a light (or array of lights) can be turned off before the value of the savings exceeds the cost of having to replace bulbs (due to their shortened operating life) will depend on the type and model of bulb and ballast. The cost of replacing a bulb (or ballast) depends on the cost of the bulb and the cost of labor to do it.
Lighting manufacturers should be able to supply information on the duty cycle of their products. In general, the more energy-efficient a bulb/light is, the longer you can keep a light on before it is cost effective to turn it off.
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Daylighting
Daylighting is the use of windows and skylights to bring sunlight into your home.
Today's highly energy-efficient windows, as well as advances in lighting design, allow efficient use of windows to reduce the need for artificial lighting during daylight hours without causing heating or cooling problems.
The best way to incorporate daylighting in your home depends on your climate and home's design. The sizes and locations of windows should be based on the cardinal directions rather than their effect on the street-side appearance of the house.
South-facing windows are most advantageous for daylighting and for moderating seasonal temperatures. They allow most winter sunlight into the home but little direct sun during the summer, especially when properly shaded.
North-facing windows are also advantageous for daylighting. They admit relatively even, natural light, producing little glare and almost no unwanted summer heat gain.
Although east- and west-facing windows provide good daylight penetration in the morning and evening, respectively, they should be limited. They may cause glare, admit a lot of heat during the summer when it is usually not wanted, and contribute little to solar heating during the winter.
If you're constructing a new house, you want to consider daylighting as part of your whole-house design—an approach for building an energy-efficient home.
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How Compact Fluorescents Compare with Incandescents
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Many compact fluorescent light bulbs now carry the Energy Star label. These bulbs last up to 10,000 hours and save $25 to $45 over the life of the bulb.
Photo credit: D and R Int., LTD. |
Compared to incandescent lamps, compact fluorescent lamps (CFLs), when used properly have the following advantages:
- Last up to 10 times longer
- Use about one-fourth the energy
- Produce 90% less heat, while producing more light per watt.
Table 1 below compares the wattage of commonly available incandescent lamps and the wattage of a CFL that will provide similar light levels.
Table 1. Comparable Wattage of CFLs and Incandescents
| Incandescent Wattage |
CFL Wattage |
| 25 |
5 |
| 50 |
9 |
| 60 |
15 |
| 75 |
20 |
| 100 |
25 |
| 120 |
28 |
| 150 |
39 |
Table 2 below shows how you can save money using CFLs. This table assumes the light is on for 6 hours per day and that the electric rate is 10 cents per kilowatt-hour.
Table 2. Cost Comparisons between CFLs and Incandescents
|
27-Watt Compact Fluorescent |
100-Watt Incandescent |
| Cost of Lamps |
$14.00 |
$0.50 |
| Lamp Life |
1642.5 days (4.5 years) |
167 days |
| Annual Energy Cost |
$5.91 |
$21.90 |
| Lamps Replaced in 4.5 years |
0 |
10 |
| Total Cost |
$40.60 |
$103.55 |
| Savings Over Lamp Life |
$62.95 |
0 |
Incandescent lamps have a few advantages over CFLs. The color rendition of incandescent lamps is superior to CFLs, though it has greatly improved in CFLs. Incandescents also project light further. This makes them more appropriate for some applications, such as for lighting in high ceilings. Compact fluorescent lamps, however, can also have advantages in high locations. CFLs can be more convenient for hard-to-reach places because they last longer and do not need to be changed as often.
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Source: U.S. Dept. of Energy
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