Daylight Autonomy 101

Specifying useful daylight deeper into the interior
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Sponsored by Lutron Electronics Co., Inc.
Jeanette Fitzgerald Pitts

Compare and Contrast the Performance of Manual and Automated Shading Systems

These shading systems can deliver significantly different results in terms of the amount of interior space that can be exclusively lit throughout the work day by daylight and the energy savings that can be generated.

Images courtesy of LMN Architects

The daylight simulations run on the LMN Architects' new office space revealed that automated shading systems created a large useful daylight zone and provided better glare control than a light shelf or pairing the light shelf with manual shades.

Compare Useful Daylight Zones

The useful daylight zone refers to the area of a building that achieves its useful daylight illuminance level at least 90 percent of the working day. It identifies the square footage of a space that could be almost exclusively illuminated by comfortable, glare-free daylight for much of the day. The type of daylight management technology used on a project has a profound effect on the size of the useful daylight zone created in the space. This was a lesson LMN Architects learned when evaluating various daylight technologies for its office renovation.

In 2014, LMN Architects undertook a renovation of its Seattle-based office. It was looking to maximize the presence of natural light in the workspace while maintaining employee comfort and saving energy. The firm ran daylight simulations to model the performance of the space when equipped with different daylight management technologies. The simulations compared the useful daylight zones achieved with light shelves and an automated shading system. The results were surprising.

The daylight simulation with the light shelf revealed high (more than 200 fc) potentially glare-causing daylight levels around much of the perimeter of the office. In the simulation, the areas receiving more than 200 fc of daylight are illustrated in yellow, and the area in red indicates a space that is always within the useful daylight range of 10 to 200 fc. The light shelf would need to be supplemented with manual shades so that occupants could work comfortably in the space. Modeling the space with a light shelf and manual shades that would overwhelmingly be left in the down position would have dramatically reduced the size of the daylight zone and the presence of daylight in the interior.

When the team modeled the use of automated shades in its space, it found that it was able to create a large useful daylight zone, free from the overly bright, glare-causing daylight that plagued the light shelf scenario. The team also ran a simulation to consider the benefit of combining light shelves with automated shades, but it created only a slight improvement and was a significantly higher cost. Ultimately, LMN installed automated shades (with local sensors) throughout the entire office.

Compare Energy Savings

With daylight harvesting products now being required in skylit or daylit areas, the increased presence of daylight in a space can immediately generate energy savings. As automated shades are able to more reliably allow greater amounts of usable daylight into a space, the systems can also deliver greater energy savings when compared to manual shades.

A recent study, completed in collaboration with Lutron Electronics and Purdue University, compared the energy savings that could result from both shading systems. An energy simulation of a perimeter private office with a lighting power density of 0.9W/square feet, standard, clear, double-pane glass, and a shade fabric with 5 percent transmittance was conducted. The study averaged the results of spaces with 20 percent, 40 percent and 60 percent window-to-wall ratios. Manual shades were defined as closed shades for the study. The team concluded that an automated shading system was able to reduce the electric light use in the private office by 83 percent, when compared to the amount of electric light used if the windows were fitted with manual shades.

In projects of any scale or application type, the effective incorporation of daylight is steadily becoming a more and more common design goal. Armed with more advanced technology and daylighting design know-how, designers today are able to adequately illuminate a space using daylight exclusively. Achieving daylight autonomy saves energy and creates a more satisfying and productive atmosphere for building occupants, which are just two examples of how a daylit workspace works harder. And with automated shading systems, no one has to lift a finger.


Lutron Electronics, headquartered in Coopersburg, Pennsylvania, designs and manufactures energy-saving light controls, automated window treatments, and appliance modules for both residential and commercial applications. Its innovative, intuitive products can be used to control everything from a single light to every light and shade in a home or commercial building.

For help with shading design, visit


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Originally published in Architectural Record