The focus on biological rhythms is important because people have been shown to respond to the natural cycle of daylight (i.e., dawn, brightening, midday, dimming, dusk, and dark) with their own circadian cycles of alertness and sleepiness. Creating artificial lighting conditions that are static and separate people from the cues that trigger their natural circadian rhythm confuses the body as to whether it should be alert or sleepy. One of the primary differentiators has been determined to be the presence of blue light in the spectrum of light color in buildings. More blue light mimics the light color of daylight (think blue, daylit skies) and signals the body that more alertness is needed. Less blue light mimics the changing color of daylight as sunset approaches and is a signal that more sleepiness is appropriate. Of course, this response is not immediate but is based on the pattern of a daily or multiday cycle, which is why changing time zones or simply changing to daylight savings time can be a challenge for many people until their bodies (i.e., their circadian rhythms) adjust.

Incandescent lighting casts a decidedly non-blue color (more yellow), but fluorescent lighting is also lacking in blue light; this lack of blue light is the condition that tells the body to prepare for sleep. Nonetheless, these have been the primary lamping choices in work environments and school buildings for years. Studies that compared workers and students in buildings with these traditional lighting systems to those in buildings with blue enhanced LED lighting or similar, demonstrated significantly better performance as a result. In some cases, dynamic lighting (i.e., lighting that can be controlled to change color spectrum over the course of a day) was used to more closely match the changing nature of sunlight across the day.

Light Color Related to Alertness and Sleep

Dr. Steven W. Lockley, Ph.D., is a neuroscientist affiliated with Brigham and Women’s Hospital and Harvard Medical School, both in Boston, and Monash University in Melbourne, Australia. He has studied and written about the implications for light color and quality related to alertness, sleep, and health. presenting on this topic at the 2018 IESNA Annual Conference and elsewhere. He sees the direct connection between lighting as designed into buildings and people’s responses to that lighting. He has also worked with NASA since the astronauts and scientists in the International Space Station (ISS) can see as many as 16 sunrises in a day, meaning that their circadian rhythms, sleep patterns, and alertness are all affected. In response, he has helped them to change out the lighting inside the ISS so it can be electronically controlled to better suit human needs. His recommendations based on this work apply directly to the design of buildings as follows.

• For buildings where people do not sleep (e.g., work environments, schools, colleges, outpatient clinics, day centers, etc.), it is appropriate to use high-intensity, blue-enriched light continuously all day. This can be applied to overnight conditions too if the building is in full operation overnight or works through shifts. This provides a safe, short-acting, and non-pharmacological stimulant to improve alertness, performance, productivity, and safety. Because there is no need in these facilities to promote sleep, dynamic lighting or the ability to tune the lighting color is not needed.
• For buildings where people sleep and live 24/7 (e.g., residences, hospitals, extended care facilities, prisons, etc.), it is appropriate to use high-intensity, blue-enriched lighting during the day to mimic natural daylight. As the day wanes, then it is appropriate to dim lighting and remove the blue enrichment gradually for as long as practically possible before sleep. (Avoiding sources of blue light for several hours before sleep has also been promoted by computer and cell phone manufacturers since their devices typically produce a blue-enriched light). This approach can help improve sleep patterns and even some common disorders, thus improving overall wellness.

In short, Dr. Lockley is noting that people respond directly to the amount, color, and timing of light as found in natural daylight. His recommendations apply to artificial lighting systems that are trying to mimic daylight and capitalize on the positive effects to help people achieve the desired results. Of course, designing appropriate daylight into buildings will achieve the intended results naturally.

Daylight and Real Estate Value

A study conducted through the Department of Architecture and the Center for Real Estate at the Massachusetts Institute of Technology (MIT) looked at “The value of daylight in office spaces” from another standpoint.¹ Specifically, while the team recognizes that the presence of natural daylight in indoor workplace environments improves human health, well-being, and productivity, it wondered if those benefits translated into economic value—that is, would office tenants pay more for a naturally daylit space than one that is not? To answer that question, the team looked at more than 5,100 different office spaces in the Manhattan borough of New York City. Specifically, it paired urban daylighting simulations of these spaces with an economic valuation model to determine if there was any correlation.

After completing the analysis, the MIT team found that, holding all other factors constant, occupied spaces with access to high amounts of daylight garnered a 5–6 percent premium in rental rates over spaces that did not have high amounts of daylight. The threshold for “high” amounts was based on spatial daylight autonomy, which is defined as a space that can function on daylight alone. In this case, if the tenant space had at least 55 percent of the area that could be modeled to function solely on daylight, it was considered to have a high amount of daylighting; less than 55 percent was deemed to have low amounts of daylighting. In the process of doing this study, the team determined that an estimated 74 percent of the office spaces throughout the dense, urban environment of Manhattan had low daylighting. Therefore, finding a space with high daylighting values becomes a differentiator, one for which the study suggests tenants are willing to pay a bit more.

Daylighting Performance Considerations

With an understanding of the significance and beneficial impacts of daylighting, we now turn our attention to the ways to achieve it in buildings. Fundamentally, there are two types of daylighting strategies: side lighting or top lighting. As the names suggest, they relate to the part of the building where daylight is designed to enter. Side-lighting uses windows, glazed walls, punched openings, or other architectural techniques to allow daylight to be directed inward from the side walls of a building. That means the users of the building will experience the daylight from one side or the other and at a height that is determined by the location of the opening in the walls. There may be some additional items such as light shelves, baffles, or diffusers that help daylight penetrate deeper or become more evenly distributed in the building sides.

Top lighting is focused on bringing daylight in from above the occupants or users of the building. Strategies to achieve top lighting can include roof openings with specifically sized unit skylights or large, monumental glazed portions of a roof. Top lighting can also be achieved through the use of saw-tooth profiles, roof monitors, or other architectural features and offsets to capture and re-direct daylight downward.

In any given building, side lighting, top lighting, or both should be reviewed as potential daylighting sources consistent with the other design parameters of the building. In all cases, there will be some common considerations to take into account as discussed in the following sections.