Daylighting Systems

Daylighting is a technique to use the natural light of the sun to light the interior of buildings.
Photo credit: Jeremy Levine

Windows, tubular skylights, and other daylighting systems can be used to bring sunlight into the building.

Daylight Harvesting

Daylight harvesting systems automatically adjust the amount of artificial light used in a building based on the availability of natural sunlight. These systems may include technologies such as lighting controls, dimmers, photosensors and and other devices. Studies have shown that daylight harvesting systems can cut energy use for lighting by 20-60%.

All daylight harvesting systems use photosensors to detect the amount of natural light, or both the amount of natural and artificial light.

Open-loop systems use a photosensor to determine the amount of daylight. Closed-loop systems use a photosensor to determine the amount of both daylight and artificial light. Both systems report the amount of light to a lighting control system, which adjusts the artificial light accordingly. Some systems are on-off systems, which simply turn the artificial light on if there is not enough daylight, and vice versa. Some systems have dimmers, which are more expensive. These systems adjust the amount of light available based on the amount of incoming daylight.

While dimming systems are more expensive, they are typically more effective at saving energy and provide more even lighting levels. With a well-calibrated system, the occupants should not notice changes in the lighting levels.

While daylight harvesting systems are shown to save energy, some users have reportedly deactivated them because they do not perform as expected.

Benefits of Daylighting

Daylighting systems allow buildings to use less artificial light because they bring natural light into the building. This not only saves energy, but has also shown quantifiable improvements in worker productivity and health.

In 2003, Carnegie Mellon’s professor Vivian Loftness released a study that showed a 3-18% increase in productivity in buildings with daylighting systems.
However, if improperly designed, daylighting can introduce too much glare, which can lead to higher, rather than smaller, cooling loads. Therefore, proper consideration should be given to all building systems when designing any type of lighting system.

Tubular Skylights

Tubular skylights are light pipes that transfer daylight from the roof to the indoors, even through considerable distances (i.e. an attic). The tubular skylight contains a (typically parabolic) lens on the roof, a reflective tube that directs the light inside, and an interior light fixture with diffuser.

3 Tubular Skylights for LEED IEQ

The following three tubular skylights are examples of models that are currently available on the market:

1. Solatube

Solatube, Inc.’s founder, Steve Sutton, is the inventor of the tubular skylight. The company, founded in 1989, offers the “Solamaster” and “Brighten Up” series of tubular skylights, meant for commercial buildings.

The Solatube 160 DS (10 in/250 mm Daylighting System) and the Solatube 290 DS (14 in/350 mm Daylighting System) with the Classic Vusion™ Diffuser or OptiView® Decorative Fixture are ENERGY STAR rated.

2. ODL Tubular Skylights

ODL’s tubular skylights, which have a solar-powered dimmer option, are ENERGY STAR qualified in all U.S. climate zones, and are NAHB Green Approved. The company’s 10” tubular skylight lights can light up to a 150 square foot space with the power of 3 100 W lightbulbs, and a 14” can illuminate up to a 300 square foot space with the output of 5 100 W lightbulbs.

3. Velux Sun Tunnel Skylights

Velux offers a range of tubular skylights for various applications. The company sells rigid tunnel models, which provide bright light and are ENERGY STAR qualified. It also offers flexible tunnel models, which are easier to install. Its pitched flashing skylights are the best for maximizing daylight harvesting, though low-profile flashing models are the most aesthetically pleasing because they blend in with the roof.

Daylighting and LEED

Daylighting could help to achieve the following credits in LEED for New Construction 2009:

•IEQ Credit 8.1: Daylight & Views - Daylight (1 point)

This credit requires daylighting in at least 75% of indoor spaces.

•EA Prerequisite 1: Minimum Energy Performance (0 points)
This credit establishes a minimum level of energy efficiency for buildings based on cost. Since daylighting reduces the use of artificial lighting, it will reduce energy costs and contribute to this credit.

•EA Credit 2: Optimize Energy Performance (1-19 points)
This credit awards points to projects that increase energy efficiency beyond the minimum in EA Prerequisite 1.

Additionally, daylight harvesting systems that have multiple dimmable controls for occupants could possibly contribute to IEQ Credit 6.1, Controllability of Systems - Lighting.

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