Proper lighting improves the function, appearance and energy efficiency of a home. It is also important to the occupants' comfort, health and safety. Yet lighting is often considered as an afterthought in the design process, with more emphasis given to wiring considerations or decorative aspects than efficiency and function.
Builders can distinguish their homes by incorporating daylighting strategies to optimize natural lighting and by increasing the efficiency of supplemental lighting. Since lighting can account for 10-25% of a home's energy use, this will make a big difference in the homeowner's electricity bills. This Tech Set provides an integrated approach to improving the efficiency and effectiveness of lighting used in and around the house.
Tech Set Details
Natural Lighting Strategies
A well designed home maximizes the use of natural lighting without compromising energy efficiency. Consider the following steps.
Locate Windows with Daylighting in Mind
Good lighting begins with the effective use of sunlight. Consider the size, location and primary function of the windows. Will the window frame a view, capture prevailing breezes, allow adequate light, provide architectural balance?
There is a tradeoff between the benefits of windows, such as daylighting and good views, and the major drawback, reduced insulation value. Because even new windows have a much lower insulation value than walls, they should not exceed 15% of the wall area, unless the home is specifically designed to take advantage of passive solar heating. With proper window placement, there should be more than enough daylighting in the home with 15% or less window-to-wall area.
Low-emittance (low-E) windows keep the heat inside in winter and outside in summer and - as a side benefit - protect furnishings from fading. They have a thin film applied to the glass that improves the performance of the window.
The two most important indicators of a window's performance are the U-factor and the Solar Heat Gain Coefficient (SHGC). The U-factor measures how well the window insulates. The lower the U-factor, the better the insulation value. The SHGC measures how well the window blocks heat from the sun. The lower the SHGC, the less solar heat the window lets in.
Each climate has optimum values for both the U-factor and SHGC. See the Energy Efficient Window Collaborative window selection tool (click on Selection Tool) to choose the right windows for the climate. Make sure to specify ENERGY STAR qualified windows, which meet or exceed your region's
Remember, the better the window, the more comfortable - and more energy efficient - the home.
Seasonal Window Shading
Provide for shade at south- and west-facing windows with an appropriate roof truss design, architectural features, landscaping plan, and decorating plan.
In warm climates, sunlight can overheat the home through windows on the south and west facing sides of homes. Roof overhangs can provide shade for these windows as well as improve the home's long-term ability to withstand rain. They also allow homeowners to open windows on a rainy day. Specify 24-inch eave and 12-inch rake overhangs when possible.
Where overhangs will not throw shade, like first floor windows in 2-story homes, architectural features like lanais or awnings can offset any potential heat gain that windows on southern and western facades might be subject to during the cooling season. Deciduous trees and vine shading can also help keep the home cool.
Window treatments like window films can also be added to windows to keep heat from the sun from entering the home, although they have the disadvantage of darkening the home throughout the day. Shades and blinds can also be closed during peak solar hours to prevent overheating.
Where windows are not practical due to elevation or a room's layout, tubular skylights can provide natural light while minimizing the size of the roof penetration.
Tubular skylights have a roof-mounted light collector that reflects light through a metal or plastic tube with a highly reflective interior coating. The reflective tube guides the sunlight to a diffuser lens mounted on the interior ceiling surface that spreads light evenly throughout the room.
They are frequently used in windowless bathrooms and closets where natural light is desirable and where skylights aren't possible because of attic space above the ceiling. They are also often installed in other dark spots throughout the house, such as hallways and stairwells. In single-story homes they can direct natural light to basements.
Follow these strategies to ensure the home's artificial lighting is as practical and energy-efficient as possible.
Develop a lighting plan
A lighting plan should include both the location and the specifications of fixtures and controls on a page of the architectural plans. Decorative, task, focal, and safety lighting should be addressed in the lighting plan and specifications, along with the ambient lighting prescribed in the codes.
Guidance may be found from professional lighting designers, who are often on staff at lighting supply retailers. Typically, these designers are architects or interior designers with a specialty in lighting. Many are fee for service consultants.
To locate a lighting designer in your area contact the Illuminating Engineering Society of North America or the International Assoc. of Lighting Designers. Make sure they are aware of the natural lighting in each room as well.
The Northwest Energy Alliance provides primers in lighting design based on room use and energy efficiency (click on
ENERGY STAR Qualified Fixtures
Specify ENERGY STAR fluorescent fixtures for substantial energy savings. Installing these products for the 5 most used fixtures will save homeowners about $60 per year.
Any objections to the glow cast by fluorescent lamps can be overcome by specifying a lamp with a higher Color Rendering Index (CRI). The CRI scale ranges from 0-100, with natural daylight representing the top of the scale. Newer fluorescent and compact fluorescent bulbs can be purchased with CRIs in the 70-90 range. Lighting experts target a CRI of 80 and above for visualizing true color.
Recessed lights that penetrate the building envelope (ceilings with attic space above) should be IC-rated (insulation contact) to signify fire-resistance and to prevent air leakage and energy loss. Other similar lighting fixtures should be caulked around the edge or gasketed to prevent air infiltration.
The Northwest Energy Alliance lists fluorescent fixture alternatives to incandescents based on fixture wattage (click on Tools/Resources, then Fixture Tool). Information on ENERGY STAR®'s Advanced Lighting Package and Seattle City Light's efficient home lighting packages can also assist the selection process.
CFLs and Full Spectrum Fluorescent Lamps
Where existing incandescent fixtures can't or won't be replaced with fluorescent fixtures, compact fluorescent bulbs can be used to reduce the electricity usage. As an example, a 60-watt incandescent bulb can be replaced with an 11 to 15 watt compact fluorescent, for roughly a 76% reduction in demand. Although compact fluorescent light bulbs (CFLs) cost more than incandescent light bulbs, each bulb saves $25 to $30 over its lifetime, and lasts 6-10 times longer than incandescent bulbs.
CFLs should be ENERGY STAR or otherwise reputable to ensure the long life that gives them a low life-cycle cost. ENERGY STAR CFLs typically are no more energy efficient than non-ENERGY STAR models, but they come with a minimum one-year warrantee, and a guarantee to not flicker, buzz, or hum.
To maximize their benefit, use CFLs in high use areas. For lights that are used for only short periods of time, specify incandescents with dimmer switches, motion sensors, or timers.
LED (light emitting diode) technology, new to the residential lighting scene, uses 90% less electricity than incandescents. Because of LED's long life and additional up-front cost, they are suggested for difficult-to-service indoor and outdoor applications, and heavily used indoor areas. They can also be used in a variety of creative lighting layouts because of their size -- roughly that of small Christmas lights.
Dimmer switches allow one fixture to serve several lighting functions, such as task lighting when at full illumination and decorative or safety lighting at lower settings. Dimming increases lamp life and saves energy because less electrical wattage is used.
Incandescent lamps last longer when a "soft-start" dimmer is installed. Fluorescent fixtures require either a dimmable ballast or additional wiring. Dimmer switches and other lighting controls are rated for total controlled wattage, type of wiring, and type of fixture (electronic ballast, incandescent, or other). Visit Elflist.com for more information.
Some fluorescent lights and fixtures may also be put on dimmers. Be sure to check the product details because dimmers will shorten the life of CFLs that were not designed for this purpose.
Outdoor lighting is installed on many homes for safety and security. Adding motion sensors to outdoor lights can increase home safety. They turn the light on when they detect movement, usually within a range of 20 feet, and automatically switch off after a set amount of time. Because they limit the time that the lights are on, they can reduce energy use by up to 90%.
Motion sensors can also be used indoors in rooms that are used for short periods of time, such as hallways, bathrooms, workrooms, garages and closets. They are convenient because they allow for the hands-free use of lighting, which can be beneficial in mudrooms and laundry rooms.
Because they keep the lights on for only short periods of time, motion sensors should not be used with CFLs.
Inform the Homeowner
Much of the benefit of improved artificial lighting will diminish if the homeowners are unfamiliar with the features. For this reason, take the time to explain the fixtures, features, and controls to the users, and describe the benefits of using these features. You should also provide information on where they can purchase replacement lamps and bulbs. Always leave all warranty and maximum wattage information with the homeowner.
The International Residential Code (IRC) requires that all habitable rooms be provided with an aggregate glazing area equal to a minimum of 8% of the room dimension with one half of that operable for ventilation.
The IRC will allow mechanical ventilation (0.35 air changes per hour per room or a formula based on prescribed occupants) and artificial light (6.46 lux covering the area at 30 inches) in lieu of the glazing requirement.
The IRC also requires electrical components, devices, fixtures and equipment to be listed for the application, bear the label of an approved agency (UL is the most widely used third party testing and certification entity for lighting), and be installed and used in accordance with the manufacturer's installation instructions.
New lighting standards have been promulgated by the State of California under the latest Title 24, mandatory for new home construction on October 1, 2005. Look for other states to follow.
California Energy Commission has specifications for state lighting standards
California Lighting Technology Center has a 'Residential Lighting Design Guide' for energy-efficient lighting.
Energy Federation, Inc. is a source for full-spectrum compact fluorescents and
International Residential Code 2003 (IRC)
Lawrence Berkeley Lab has information on windows and daylighting.
Natural Lighting is a source for full-spectrum light bulbs.
National Fenestration Rating Council (NFRC)
The Rensselaer Polytechnic Inst. Lighting Research Center
Top Bulb is a source for full-spectrum fluorescent tubes.
Underwriter’s Laboratory (UL)