Lighting

People spend most of their lives indoors in industrialized countries, so lighting becomes an important drain on a power grid. Lighting comes in two forms, natural sunlight and electrical, and each of these can be managed in a way that increases the overall energy efficiency of a home.

The most efficient use of natural sunlight is called daylighting. Daylighting integrates natural light with electrical light to create the best indoor lighting conditions as well as to save energy. Daylighting usually involves the following four main structures for maximizing the amount of sunlight that enters a structure:

1. light pipes—roof to ceiling tubes, about 13 inches (33 cm) in diameter, that can light about 200 square feet (19 m2) of space with sunlight
2. skylights—large, rectangular rooftop windows
3.  clerestory windows—narrow horizontal windows set high into walls
4. light shelves—horizontal platforms that redirect light hitting a large south-facing window so that the light penetrates deeper into a room

Daylighting is an energy-saving technique that reduces the need for electric lights during the day. Many techniques aid daylighting. A clerestory or a light shelf each reflects light deeper into the house’s interior. Special glazes on wall surfaces also help reflect light into rooms.

 The daylighting structures mentioned here provide benefits to the home in addition to bringing in more light. For instance, clerestories opened in summer let hot air out, and if they are made of well-insulated glass they hold in warm air in the winter. Light shelves expand the available light to make electrical lighting almost unnecessary during the day, and they reduce glare. The Lawrence Berkeley National Laboratory has estimated that light shelves can expand the indoor daylight zone 2.5 times the window height.

Improved morale and even health may be added benefits that come from daylighting. Students in classrooms and office workers have better attention, memory recall, and productivity in daylighted rooms than people in rooms with only artificial light. Building designer David Hobstetter wrote in a well-researched 2007 article in Real Estate News, “Our lives have become increasingly sedentary and cloistered over the past few decades, with the rise of the digital age. As a species, we now pass the vast majority of our time indoors . . .” Hobstetter attributed increased stress, fatigue, absenteeism, and even work-related illnesses to poor indoor working conditions, including a lack of natural light. A Toyota employee put it in simpler terms when talking with the Los Angeles Times reporter Roger Vincent, “The [natural] lighting is easier on the eyes and on the nerves. It’s pleasant and feels more productive.” Daylighting therefore has psychological advantages to complement health and energy-saving benefits.

The compact fluorescent lightbulb
demonstrates that not all achievements
in environmental engineering need be
complicated to have a positive effect
on the environment. By redesigning
normally long, straight fluorescent
lighting into a compact size about the
same as an incandescent bulb, engineers
introduced an energy-saving product for
homes and offices.

Electrical lighting serves as a substitute for natural sunlight and offers the following advantages over sunlight: (1) it can be turned off; (2) it can be dimmed or made to produce high intensities; (3) it can be selected in different colors; and (4) it provides light in places where sunlight cannot reach. The best way to improve energy efficiency in electrical lighting is to replace all standard incandescent lightbulbs with either compact fluorescent (CFL) lightbulbs or halogen lights. Incandescent bulbs emit only 10 percent of their energy as light and 90 percent as heat, meaning they are very inefficient at converting electrical energy into light energy. CFL bulbs cost more than incandescent bulbs, but they last 10 to 20 times longer and use 75 percent less energy. The following table summarizes the impact of CFL bulbs on energy savings by using the U.S. Environmental Protection Agency’s (EPA) and Department of Energy’s (DOE) joint Energy Star online calculator.

Each incandescent bulb replaced by a CFL bulb reduces the CO2 emissions from power plants by several hundred pounds over the bulb’s useful life. If each U.S. household replaced one light, CO2 emissions would drop by more than 1 trillion pounds (454 billion kg). Halogen lighting does not save as much as CFL bulbs, but halogen lighting is still about 50 percent more efficient than incandescent lighting. All types of electrical lighting can be made more energy efficient by using light sensors to dim or turn off lights on bright days and timers to turn off lights automatically.

The U.S. Congress has voted to follow the lead of the European Union, Australia, New Zealand, Japan, and Brazil in banning the sale of incandescent lightbulbs beginning in 2012. According to the plan, the United States will have phased out all incandescent lightbulbs by 2014.