Insufficient daylight coming through the windows of your house, apartment or workplace may be worsening your health. At night, electrically powered sources of light may further compromise health. And researchers suggest that perhaps as many as a third of the people reading this newspaper might be affected.

Problems with sleep, mood and alertness are the primary, light-related symptoms. These symptoms result from the conflict between the human brain’s natural diurnal clock — the circadian rhythm triggered by and linked to rising and setting of the sun — and the actual timing of day-to-day activities. If your sleep-wake schedule is substantially out of sync with your work-play schedule, you probably suffer from some or all of these symptoms.

Decades of research in chronobiology show that the timing, intensity and duration of exposure to daylight and darkness directly affect how well people sleep, how well they function while awake and how well they feel.

SAD — seasonal affective disorder — is an appropriate acronym. Anecdotal evidence has long told us that living in extreme, sun-deprived northern latitudes, such as Scandinavia, can induce depression. Inhabitants of northerly American and Canadian cities with lengthy, cloud-overcast winters commonly complain about how their city and their moods are gray for too many months.

In their recently published book “Chronotherapy: Resetting Your Inner Clock to Boost Mood, Alertness, and Quality Sleep,” authors Michael Terman and Ian McMahan explain in detail the relationship between health, light and architectural design, and specifically the design and treatment of windows and lighting systems in buildings.

Shaping the City (Roger K. Lewis)

The authors point out that millions of America’s dwellings, offices and factories have insufficient sources and amounts of daytime light from windows, or from electric fixtures in spaces where windows are remote or lacking.

Many traditionally styled residences and residential buildings have windows that are too small and too few. Interior window treatments — blinds, shades, drapes — installed by occupants may further reduce the amount of available daylight, especially in the morning when exposure to bright light levels is most essential for waking the brain and triggering its daytime clock.

After dark, many people then sit too long in front of light-emitting TVs, computers and digital tablets when the body’s circadian system is signaling that it’s time to go to bed. Intermittent drowsiness and dozing, well after secretion of sleep-inducing melatonin hormone, should tell us that late-night light exposure and activity, especially snacking, are unhealthful habits.

Chronotherapy entails several strategies and treatments to improve chronobiological health. One obvious strategy concerns architecture: Establish scientifically based standards for designing windows to admit ample quantities of natural daylight, along with standards for healthy indoor electric lighting.

Fortunately, health-oriented window-design standards will synchronize well with sustainability design standards. The latter pertain to use of daylight and solar energy to reduce energy consumption and carbon emissions. High-performance curtain walls and energy-efficient glass make this marriage even more desirable.

Daylight as well as electric lighting can be employed explicitly to enhance synchronization of real-world and circadian schedules, thereby remedying sleep and mood disorders. Sitting in front of a properly designed “light box” for brief, prescribed periods can advance or retard the brain’s sleep-wake cycle, enabling internal time patterns to match external time patterns.

Other factors determine the impact of daylight and the need for light treatments. Effects vary over the year with seasonal and climatic changes that affect sunlight. Genetics play a role, as do an individual’s physiological conditions and age. Children, adolescents, middle-aged adults and aging seniors have very diverse circadian rhythms and sleep requirements.

Within buildings, room placement and room orientation matter. For example, to harvest early morning sunlight, bedrooms and breakfast areas ideally should face east or southeast rather than north or northwest. Research has shown that patients in hospitals, nursing homes and extended-care facilities fare better physiologically and physically in spaces with generously proportioned windows providing pleasant views as well as ample daylight.

Filling residential and office interiors with natural light while capturing views has long been a design objective for many modernist architects. Creating bright, open interiors is also why many architects tend to prefer white, light-reflective wall surfaces. This characterizes my house, designed more than 40 years ago with large amounts of glass, including high clerestory windows and a skylight, and without blinds, shades or drapes.

Although motivations were and continue to be primarily aesthetic, I and many architects designed buildings instinctively believing that interior spaces filled with daylight are inevitably salubrious and mood-enhancing. Thanks to chronobiological research, scientific evidence now confirms that belief.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland. His cartoon may be seen at