Daylighting systems harvest natural lighting and automatically adjust electric lighting based on the amount of ambient light. These systems offer the potential to cut energy use, reduce peak demand, and create a more desirable indoor environment.

Depending on your building’s location and orientation, a daylighting system has the potential to save 20% to 40% of your energy use. However, getting the system to live up to its potential lies in:

  • Combining a well-designed control system with commissioning (testing and calibration)
  • Effectively coordinating the efforts of your entire design team
  • Training occupants on how to use the systems

What are the options?

Daylighting installations fall into two categories: top lit and side lit (figures 1 and 2). Top-lit systems use skylights or monitors (a raised section of roof that includes a vertical window) to bring in light from the top of a building. Side-lit systems let daylight in through windows or other openings on the sides of the building. Building architects use light-guiding systems such as louvers, light shelves, and reflective walls and ceilings together with daylighting systems to reflect or redirect sunlight in the space.

Figure 1: Simple daylighting techniques

This schematic shows a mix of top lighting, side lighting, light shelves, high-reflectance ceilings, and wall diffusion to provide uniform deep-plan daylighting without the glare of direct sunlight.

Diagram showing daylight coming in through acrylic glazing in the ceiling that reflects off the walls to different levels in a building. Daylight also comes in through a window and bounces off a light shelf to reflect off the ceiling to light the room.

Figure 2: Daylighting in action

Top and side lighting let in daylight at this airport facility.
Photograph of light coming in through windows in the ceiling and on the wall in an airport.

It’s easier to get top-lit systems to work well than it is for side-lit systems. In top-lit systems, the light shines from above and creates uniform lighting on horizontal work surfaces and walls, similar to electric lighting. In comparison, side-lit systems, which bring daylight from the side of a building, may not create uniformly lit work surfaces. Also, daylight doesn’t penetrate as deep into the building with side-lit systems, and occupants need window treatments such as shades or blinds to prevent glare.

You can use open-loop or closed-loop controls for either approach. Open-loop systems monitor only the incoming daylight and adjust the electric lights based on the available daylight. In a closed-loop system, photosensors monitor both daylight and electric light to automatically adjust the electric lights depending on the total amount of light available in the space.

You can adjust light levels with dimming controls or turn on or off lights with switches. Switches are simpler to operate, lower in cost, and easier to commission, but you may not like the drastic change in light levels. Dimming controls are more expensive, but you may prefer the more gradual change in light.

How to make the best choice

Achieving an effective daylighting system requires careful planning and installation as well as postinstallation measures such as commissioning and training. Online, you can find several resources on the design and installation of daylighting systems (figure 3).

Figure 3: Daylighting programs

You can use these resources when you work with building architects and lighting professionals to design an effective daylighting system.


Program Description Website
  © E Source
Daylight Dividends Daylight Dividends was established to promote daylighting as a way to improve indoor environmental quality. It focuses on overcoming technological barriers to the effective use of daylight and supporting state and regional efforts at market transformation. www.lrc.rpi.edu/programs/daylighting/index.asp
Daylighting The Whole Building Design Guide explains daylighting terminology and recommends design considerations. www.wbdg.org/resources/daylighting
DayLighting Collaborative DayLighting Collaborative encourages the use of daylighting in buildings. It provides education, training, and other resources to advance the technology. www.daylighting.org
Radiance Radiance is a free, open-source software for simulating solar controls, lighting, and daylighting designs. www.radiance-online.org

Make commissioning part of the process from the beginning Commissioning your daylighting system consists of adjusting photosensors and ensuring proper sensor placement so your electric lighting system responds properly to daylight. However, today’s analog sensor technology allows for more values than the digital sensors offer. Adjustments can be tricky, and calibration is more art than science. But you can find sensors that can self-calibrate or products that remotely calibrate the sensors to make commissioning easier.

Keep your daylighting system simple Making a daylighting system as straightforward as possible may mean sacrificing potential savings, but uncomplicated systems are more likely to work correctly. Typically, simple means using fewer sensors, choosing open-loop controls, and using on-off switching. Top-lit systems are simpler than side-lit systems and can more often use simple on-off controls instead of dimming.

As we mentioned above, switching lights on or off can make changes in light levels more noticeable. Multilamp fixtures—where you can turn individual lamps on or off—make light switching less noticeable. Indirect lighting is another way to subtly change light levels because the light distribution doesn’t change as much when you turn off one or more lamps.

You can also use cheaper, more-efficient instant-start ballasts for on-off switching. But be wary of units that combine occupancy sensors and photosensors in a single package. While they’re becoming more common, the two types of sensors often have different positioning requirements.

Coordinate the efforts of all design professionals To build a good daylighting system, all members of your design team—architects, interior designers, mechanical engineers, and commissioning agents—need to coordinate. For example, if the interior designer isn’t on the team, you may wind up with interior furnishings that are too dark for the planned daylighting system. If mechanical and electrical specialists aren’t aware of the benefits of a planned daylighting system, they may not size HVAC equipment correctly to take advantage of the reduced cooling loads, meaning the controls are less likely to work effectively.

Require good analytical models Because the direction and intensity of incoming daylight change every day, most experts recommend using computer simulations to design daylighting systems. Researchers from the National Renewable Energy Laboratory suggest that designers make their models as accurate as possible, taking into account weather patterns, office furniture and layout, and trees or landscaping that may block sunlight.

Check that your daylighting designers simulate glass properties correctly; specify frames, mullions, and window screens to accurately estimate the incoming quantities of light; and consider the effects of exposed structural elements, such as columns and beams, as well as the eventual contents of the space. Also, make sure that architects periodically review parameters such as window size, glazing, and shading to update building models accordingly.

Supplement daylighting with task lighting Strategic use of task lighting can enable deeper dimming (25% to 30% of maximum output) of ambient lighting.

Work closely with manufacturers, building operators, and contractors Working with building operators, contractors, and equipment manufacturers can help you avoid problems such as installing the wrong number of sensors or calibrating the system improperly. In one study of top-lit installations, researchers found that projects where the controls supplier had a continuing relationship or service contract with the building owner yielded the best results.

Ask for good controls documentation Your controls documentation should include a set of accurate and detailed instructions for occupants and building operators.

What’s on the horizon?

Researchers are developing new technologies to bring daylight deeper into buildings—even into spaces that may not have windows. These systems use mirrors that track the sun and focus the sunlight, while fiber-optic cables transport the sunlight to where it’s most effective.

Who are the manufacturers?

Neither this list nor any mention of a specific vendor or product constitutes an endorsement or recommendation by the authors, nor does any content in the Business Energy Advisor constitute an endorsement or recommendation, explicit or otherwise, of the technology-related programs mentioned herein.

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