Earlier this year, a team from the DC office of Perkins+Will was awarded a micro-grant through the firm’s Innovation Incubator to investigate ways to improve lighting in an open work space. Six DC colleagues used the office’s existing lighting control and energy management software to study the impact of several lighting power reduction strategies, with particular focus on actual energy usage and occupant comfort and productivity. The resulting report, Lighting and the Living Lab, provides insights on how the office’s lighting system could be improved. These lessons learned can also be applied to the design process for clients in the future.
The team focused on three lighting strategies: task tuning, load shedding, and daylight harvesting. The first strategy, task tuning, examines adjustments to lighting levels based on the type of work being done. Fixture intensity is adjusted over time so spaces are not over-lit, which wastes energy. In the second strategy, load shedding, an energy threshold is pre-established. Once the designated space reaches that level of energy use, certain non-essential light fixtures are automatically turned off or dimmed to conserve energy. The third strategy, daylight harvesting, looks at bringing increased natural light into a space that is supplemented with light fixtures as required in order to reach a predetermined light level. Our original study ran for twelve weeks in June, July, and August; the team plans to conduct a second study in the winter months due to the impact of seasonal variations on light.
The open studio space in the DC office was the site for the study. The space has a large window façade facing due east. There are smaller windows on the north and south sides of the studio and some light coming from a building atrium to the west.
The following is a short summary of what we learned.
Not every strategy will work in every space. No two spaces will have exactly the same solar orientation, either because of the building’s own placement or the heights of neighboring buildings. It is extremely valuable to do an in-depth lighting analysis that examines the unique physical properties of the space and needs of the occupants. Especially if a project team is investing in a lighting control system, it is worth the time and money to conduct a detailed lighting analysis for the space.
Don’t be timid about combining strategies. Daylight harvesting and task tuning can be intertwined carefully, for example, to maximize energy conservation in a space. Also, load shedding can mean turning off lights or dimming them in combination with the amount of natural light harvested at specific times of day.
The task sets the stage. Occupants working on computers were generally comfortable with much lower foot-candle levels on their desks than those engaging in “heads down,” paper-oriented tasks. Individuals working with paper recorded little to no discomfort from daylight glare, which was a frequent comment by those working primarily with computers.
Direct daylight and computer screens can be a tricky combination. If glare issues can be resolved through workstation orientation or the addition of simple glare screens, daylight can be brought deeper into a building’s floor plate than the LEED-prescribed minimum of 15 feet. This allows for even greater energy savings as daylight can partially replace electric lighting.
Occupant behavior can be surprising. A good workplace design that includes lighting considerations requires an understanding of what the occupants do on a regular basis. For the design to be successful, the lighting must respond to those needs. As an example, we were surprised to find that no matter how low the electric lights were dimmed in our studio, very few people bothered to use their task lights.
Keep your occupants informed. People are more likely to play a part in shifts in their environment if they understand the process and its goals. Our team used various messaging techniques to convey the purpose and methods of the study, and we followed up several of the testing rounds with short surveys. Responses by the staff clearly varied depending on our messaging. When they were not previously informed of the testing, some staff members reported experiencing lighting changes that hadn’t occurred (“You turned off the lights over my desk!”). When the staff was told ahead of time about upcoming changes, they were generally cooperative and even curious to hear the details of our findings.
Overall, our study showed that our baseline lighting scheme is already very efficient; it only accounts for 15% of the energy use in the office. By making the adjustments suggested from the experiments, we can reduce our energy demands even further. From the baseline energy use as recorded by the office energy management software, task tuning afforded a 10% reduction in lighting energy and enhanced daylight harvesting resulted in an 8% reduction. Load shedding also resulted in an energy savings; though with mechanical systems being such a large component of office energy use, the amount shed in lighting alone does not make a significant contribution to conservation. By investing resources into this study, our office will save even more resources (both financial and environmental) in the future.