Light shelves on a south facing wall reflect daylight further in to the interior of the space. Image courtesy of NREL
Artificial lighting can account for up to 15% of a building’s annual electricity use. Use of current lighting technology and designing to minimize the need for artificial lighting can decrease lighting energy use in buildings by 50-70%.

Green lighting design matches the amount of quality of light to the function of a space. Sections of lighting for different areas or different functions should be on separate controls, to allow users of a space to decide how much light is needed. Task lights should be installed where needed, and ambient light reduced elsewhere. Occupancy sensors that automatically turn lights on and off as needed can reduce energy use while having a minimal impact on building occupants. Opportunities for daylighting should be maximized, while controlling glare and unwanted heat gain.


Use of daylight in a building reduces the need for artificial lighting, and is believed to have a beneficial effect on building occupants. Good daylighting primarily uses soft, diffuse sky light and reflected light rather than direct sunlight, especially during the summer.


South facing windows with appropriate overhangs provide indirect light in the summer, and both heat and light during the winter. East and west facing windows let in light during the morning and evening, but may cause glare and admit heat during the summer. North facing windows can also be used for daylighting, as they admit relatively even, glare-free light and almost no unwanted summer heat gain. The number, size and glass type of north facing windows should be carefully considered, however, as they do not contribute to passive solar heat gain in the winter, and lose more heat than insulated walls.

Clerestory windows flanking either side of the cooling tower at Zion Visitor's Center in Zion National Park, Utah. Image courtesy of NREL.
Reflected Light

Reflecting light reduces glare and allows it to reach areas that would otherwise lack natural light. Simply painting interior walls and ceilings a light color can help provide reflected light. Light shelves are a good strategy for providing shade for south facing windows and reflecting light deep in to a space.

A light shelf is a horizontal light reflecting overhang placed above eye level with a transom window placed above it. External shelves are more effective at providing shading than interior shelves, but a combination of the two will work best to provide even lighting.

Clerestory Windows:

Clerestory windows are vertical windows near the top of a wall. They bring light in high up in a room and illuminate the ceiling. The reflected light from the ceiling is a soft, indirect light and mimics skylighting. They also allow light to penetrate deeper in to room than windows set at a standard height, especially when used in combination with adjacent light colored overhangs and light colored ceilings.

Types of lighting:

Compact fluorescent bulb. Image courtesy of NREL.

Fluorescent bulbs use 25%-35% of the electricity used by incandescent bulbs that give an equivalent amount of light, and fluorescent bulbs last up to 10 times longer than incandescent bulbs. There are two types of fluorescent bulbs: compact fluorescents and fluorescent tube/circline lamps. Straight tube fluorescent bulbs are installed in a dedicated fixture with a built-in ballast, while compact fluorescent bulbs can be used in standard fixtures. Tubular fluorescent bulbs are most common in large indoor spaces, while compact fluorescent bulbs are more common in residential spaces.

Light Emitting Diode (LED)
LED is currently one of the most efficient and rapidly developing lighting technologies. Residential LEDs uses 25% of the electricity of incandescent bulbs, and last up to 25 times longer. LEDs emit almost no energy as heat – in contrast, incandescent bulbs release 90% of their energy as heat, and compact fluorescent lights (CFLs) release up to 80% of their energy as heat. LED products are currently not as widely available or inexpensive as CFLs or incandescent bulbs, but are becoming more so all the time.

High intensity discharge (HID) lamps
HID lamps are currently the most efficient available lighting, and can save up to 75%-90% of lighting energy when they replace incandescent bulbs. HID lamps take up to ten minutes to produce light when first turned on. For that reason, and the intense light that they produce, they are most ideally suited to outdoor lighting and large indoor areas where lights stay on for at least an hour at a stretch. They are not suitable for use with occupancy sensors.

Lighting Controls:

While most people recognize that turning off lights saves energy, it’s easy to forget or fail to notice that lights are on and not being used. Lighting controls can reduce energy use by automatically turning lights on and off as needed.

Photosensors and motion detectors are most commonly used with outdoor lighting. Photosensors can be used to prevent outdoor lights from operating during the day, while motion detectors can turn lights only when they are needed.

Occupancy sensors are generally used indoors to turn lights on when a person enters a room and turn them back off when no activity is detected for a period of time. Occupancy sensors need to be located where they will detect occupants or activity in all parts of the room.