Our Built Environment Has Evolved Faster than Humans: We are Still Outside Animals

9 Jul 2026

A blog on usglassmag.com by Helen Sanders

Lisa Heschong, renowned daylight researcher and author of “Visual Delight in Architecture,” gave a presentation at the Fenestration and Glazing Industry Alliance’s (FGIA) Virtual Summer Summit to update us on new research further demonstrating the importance of daylight exposure for human health. This blog summarizes this important information and highlights the main takeaways.

Daylight Eats Electric Light for Breakfast

New data underscores that humans, who have evolved little since our hunter-gatherer days, still need exposure to full-spectrum daylight, ultraviolet (UV) and visible and near-infrared (NIR), to achieve and maintain optimum health and wellness.

However, our 21st-century way of living is not aligned with this basic human health need: Approximately 90% of our time is spent indoors, and our modern built environment does not support consistent delivery of appropriate intensity, full-spectrum daylight.

A new approach to our built environment is needed, which both encourages us to spend more time outside and delivers better daylit indoor environments.

New Data Correlating Health with Daylight Exposure

Heschong highlighted a series of recent studies of over 80,000 adults who wore light-tracking devices in the United Kingdom. After six years, researchers found that those with the highest 25% of daytime light exposure had:

The best mental health
The best cardiac health
The lowest cancer rates
The lowest mortality rates from all causes

Exposure to Daylight Indoors is Better than Electric Light

Even more significant is a first-of-its-kind study by a Dutch group, reported this January, investigating the metabolic indicators of elderly diabetic occupants who spent one week working in a daylit office versus another week in a purely artificially lit office.

The authors postulated that, because daylight is the main driver of our circadian rhythms, the “chronic lack of natural daylight could be considered as a risk factor in society’s rising incidence of metabolic diseases.” After only one week in the windowed office, participants had positive improvements in glucose level control and other metabolic processes compared to after the week spent in the artificially lit office.

Heschong noted that, while this was a small study, it provides the first direct, carefully controlled medical evidence that indoor daylight exposure may improve glycemic control in patients with Type 2 diabetes.

This is significant for our industry because it clearly shows the benefit of real daylight indoors rather than modern electric light.

In the battle for the wall, demonstrating the importance of access to real daylight in buildings is critical to counter arguments that windowless buildings lit with circadian LEDs are sufficient for human health.

New Biological Processes and Pathways:

Heschong recommended a newly published book by journalist Rowan Jacobsen, “In Defense of Sunlight,” which provides a summary of the benefits of sunlight exposure. In his book, he identifies:

42 symptoms and diseases that can be positively impacted by sunlight exposure, such as wound healing, inflammation, memory and cognition, diabetes, dementia, anxiety, obesity, etc;
15 different mechanisms in which those impacts can occur;
8 different wavelengths of light that trigger those mechanisms; and
3 different exposure routes: through the eyes, through the skin and through the whole body.

Jacobsen’s advice: “Get sun. Not too much. Go outside.”

UV Light Exposure May Not Be as Bad as We Have Previously Been Told

Jacobsen’s book also reviews the research of dermatologist Prof. Richard Weller, chair of medical dermatology at the University of Edinburgh. Weller is campaigning for health authorities to revise their recommendations that we all need to assiduously avoid sunlight exposure, guidance introduced in the 1980s to reduce the risk of deadly skin cancers.

Skin cancer deaths attributable to sun exposure are quite rare, representing less than 1% of all cancer deaths, and occur only among very light-skinned people. Furthermore, UV light has been shown to improve cardiovascular health and immune response. Thus, Weller asserts that increased exposure to sunlight has a much higher benefit in reducing deaths overall, including from other cancers and cardiovascular disease. In the case of the U.K. population, Weller has stated, “Sunlight avoidance sufficient to prevent one melanoma death would cause 45 excess deaths from all other causes.”

Myopia and UV-Short Wavelength Visible Light

Since Heschong spoke to FGIA in 2021, more information has become available regarding the link between short-wavelength light exposure (380-430 nm) and the myopia epidemic in children. She reported that, historically, childhood myopia used to be detected between the ages of 10 and 16, but now it is being detected much earlier, as early as age 6, with progression stopping at a much later age. Currently, 30-40% of U.S. teens are myopic, and in some parts of East Asia, the number is closer to 70-90%, compared to only 20-30% three generations ago. At current rates, predictions suggest 50% of all adults globally will be myopic by 2050.

The myopia epidemic has been shown to be caused by environmental factors, not genetics. Myopia is most strongly associated with reduced time outdoors, and early in-life exposure to daylight reduces the risk of developing it. Recent studies have shown that exposure to violet light (short wavelength visible light) and bright daylight early in childhood reduces the risk of developing myopia later.

While causation is still being understood, the correlation data are significant enough for the International Myopia Institute to recommend that children spend a minimum of 8-15 hours per week outside to reduce the risk of developing myopia.

Understanding how daylight exposure is critical is still crystallizing, with a focus on two new light-sensitive proteins, called “opsins,” found in the eye and skin that respond to specific wavelengths of light: ~430 nm (blue-violet visible light) and 380 nm (violet/UVa). Scientists believe these opsins (with exposure to light around those specific wavelengths) may be responsible for infant eye development, myopia prevention, core body temperature regulation and metabolism regulation.

Does NIR Light Exposure Matter Too?

Ever heard of “red light therapy?” This is an area where the explosion of product marketing claiming a wide range of health benefits may be getting far ahead of scientific understanding, according to Heschong.

A hypothesis has been developed that suggests that NIR light (700-2500 nm) is absorbed by cell mitochondria, which then boosts the production of energy through improved Adenosine Triphosphate (ATP) production. ATP is the energy source of a cell. Researchers noted that the use of LED and fluorescent lights in buildings typically has a dominant wavelength in the visible spectrum around 550 nm with essentially no NIR or UV component. Similarly, the highest performing low-e coatings also dramatically reduce the transmission of NIR and UV in energy-efficient fenestration (see figure 6).

This may have some unfortunate consequences for occupants in modern buildings. More research is needed to understand dosage and health implications before any guidance can be provided to building designers and the fenestration industry.

Light Exposure at Night Can Be Counteracted by High-Intensity Daylight Exposure During the Day

We already know that melatonin is the key hormone that synchronizes the body clock and effectively manages associated metabolic, immune, cardiac and other key biological rhythms. Heschong called melatonin the “master body-clock conductor.” Melatonin production is triggered by the absence of (sky) blue light, and so exposure to blue light at night, from screens or electric lights, suppresses melatonin production and is associated with numerous chronic diseases.

However, new evidence shows that exposure to bright enough daylight during the day helps to counteract the negative impact of light exposure at night. While the precise dosage (intensity, timing, duration, wavelengths) for daylight exposure for different groups of people has yet to be determined, ample daylight exposure contributes to better health.

Takeaways

To stay healthy, we need to:
- Spend more time outside each day; and
- Consciously design our buildings to offer appropriate levels and a spectrum of daylight to occupants throughout the day.

Both are needed. As a population, we are unlikely to change our daily activities to spend all daylight hours outside. And, it is likely not possible to design or redesign all buildings to deliver the full intensity of daylight spectrum needed consistently. However, adjustments in both behaviors and building design could deliver significant public health benefits.

The lighting industry is eating our lunch.

According to Heschong, over the past two decades, the electric lighting industry has actively worked to understand circadian daylight and developed products to artificially deliver simulated daylight, including dynamic spectrum changes. She noted that even some of their advertisements feature windows bringing in daylight, but do not show their own electric lights! Several LED light fixture manufacturers are now marketing products with output in the NIR, getting on the red-light therapy bandwagon and claiming, “We can bring daylight indoors!”

Our industry has an opportunity to design products to support full-spectrum daylight exposure indoors and with higher transmission of both short and long wavelengths.

The challenge is managing the competing need for building energy efficiency. High-performance, energy-efficient low-E coatings by design cut out a significant amount of NIR and reduce short wavelength transmission (see figure 6).

Can Glass Work Miracles?

My first thought is that we have an over-constrained problem to solve and that glass, while a remarkable material, cannot work miracles.

However, Heschong noted that for decades, designers and code requirements have relied heavily, some might say too heavily, on solar control glass coatings; yet there are many other passive and active design strategies that could be employed, such as exterior shading, orientation-based design, automated blinds, etc. She also noted that not all spaces in buildings would need to have access to higher levels of sunlight. She suggested increasing access to sun-friendly areas, such as balconies, roof gardens, atria or solaria.

By taking a different approach to building and façade design, and with access to appropriate coated glass products, solving the energy and human health problems may not be mutually exclusive. We need to open the door to new approaches to managing energy flows through fenestration that balance human health with other design goals, such as construction cost and environmental concerns.

Call to Action

Heschong encouraged the fenestration industry to:

Educate ourselves – help stakeholders to understand the importance of access to daylight indoors, as well as to outside spaces;
Lead the conversation – take back ownership of healthy lighting from the electric lighting industry and drive the narrative through stakeholder education and marketing. She suggested a “Got Daylight” campaign, which is aligned with the “Got Great Windows” proposal from the Façade Tectonic Institute’s market transformation blueprint;
Support research – to understand indoor daylight dosage needs by building type and underscore that electric light cannot provide comprehensive health benefits with similar efficiency; and
Demand our codes address daylight access for public health – to ensure every new building has sufficient daylight to support human health for generations to come.