The sunny side of daylighting
It is a simple formula—healthy employees are happy, and happy workers are productive.
Many employees feel more productive when they have adequate exposure to sunlight. This assertion is backed up by a number of studies that have analyzed the relationship between exposure to sunlight and a productive work environment for employees.
Researchers at the interdepartmental neuroscience program at Northwestern University, Illinois, reported that the detrimental impact of working in a windowless environment is a universal phenomenon. The study concluded there is a strong relationship between workplace daylight exposure and office workers’ sleep quality, activity levels, and overall quality of life.
Sunlight, or the lack of it, can have a profound effect on circadian rhythms, which are biological, mental, and behavioral changes following a 24-hour cycle and responding to light and darkness within an organism’s environment. Circadian rhythms are produced by natural factors within the body, but are mostly affected by signals from the environment. Light is the main cue influencing circadian rhythms. Figure 1 shows normal circadian rhythms based on the natural pattern of day and night.
A study conducted by the German researcher Mirjam Muench compared two groups of people—one exposed to daylight and the other to artificial light—over the course of a couple of workdays. Muench found cortisol levels drop significantly under artificial lighting conditions. This means artificial or poor lighting can actually make workers more stressed.
A study done at a warehouse for a cereal maker in Salt Lake City, Utah, found windows and skylights noticeably improved worker performance. The increase in natural lighting led to lower absenteeism and fewer product defects.
In addition to the benefits of natural light, just having a view of the outdoors improves worker performance. Two different studies conducted in the Sacramento (California), municipal utility district offices found a clear link between employees having a view to outside from their workstations and their performance.
Another study conducted by the University of Oregon, Portland, analyzed the impact an outdoor view had on the percentage of days of work missed due to reported sickness (Figure 2). Group 5 had no view, while Groups 1 and 2 had the best views of the outdoors. As Figure 2 demonstrates, the combination of the outdoor view and the effects of sunlight made workers feel good to the point of improved attendance.
Designing for daylighting
According to a white paper from ETC, an architectural lighting controls firm, as daylighting for energy savings and conservation becomes a common design practice, daylight harvesting, will be required by some energy codes. Daylight harvesting is an advanced lighting approach that uses sensors and controls to adjust the interior lights to maintain a desired light level. ETC notes daylight harvesting will soon be adopted by other energy codes—over time, it will be required for new construction and, where possible, added to existing buildings.
California’s Title 24, the International Energy Conservation Code (IECC) 2012, and The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1, Energy Standard For Buildings Except Low-Rise Residential Buildings, already have daylighting guidelines; these are likely to become mandatory nationally. Most commercial buildings with windows and skylights are required to have some type of daylight harvesting control in the adjacent area.
There are three main approaches for optimizing the effects of daylighting. One is building design, and other through interior features and systems.
Building design
This involves positioning windows for best exposure to sunlight. Building design can include skylights and clerestory windows. Optimizing the building orientation and footprint is also a tactic.
Interior features and systems
Image courtesy Lighting Design Lab
Design professionals can include daylight redirecting devices, daylighting-responsive lighting controls, and interior design focusing on placement of furniture and room surface finishes.
Systems adjusting to the available lighting from the sun
Static building positions and interior features can optimize the effects of sunlight. Given the sun’s position, time of year, and the presence of clouds—sunlight will change during the day. Ambient light sensors combining photopic, human-like sensitivity with wide dynamic range are enabling a new generation of lighting controls that may be built directly into replacement lamps and luminaires to take advantage of available daylight and shift more of the interior lighting burden away from artificial sources.
Consequently, controls throughout the day can adjust LED light levels to compensate for changes in the position and intensity of the sun. Figure 3 depicts the relationship between time of day for sunlight, LED light levels, and energy savings.
