Sunlight – direct, life-affirming, and biologically vital, is quietly being designed out of our buildings. Regulations, carbon metrics, and cost pressures are converging in ways that risk marginalizing one of the most essential elements of healthy living.

Walk through any new office development or residential tower today, and you'll notice something: rooms feel dim despite large windows, spaces lack warmth even on sunny days, and occupants gravitate toward the few spots where actual sunbeams penetrate. This isn't accidental, it's the result of design decisions that prioritize energy performance over human performance.

In a recent conversation on the podcast Sunlight Matters, I spoke with Dr. Niko Gentile, a senior lecturer in Building Physics at Lund University, and Agnieszka Czachura, one of his PhD students, about what he sees as a growing imbalance in how we design for daylight and sunlight. His message was clear: the built environment is at risk of creating spaces that work for carbon calculators but fail to meet the needs of the people who inhabit them.

Listen to the full podcast episode here:

The Daylight/Sunlight Divide

One of the most essential distinctions Gentile makes is between daylight and sunlight. Daylight refers to the diffuse natural light that you get even on a cloudy day. It's been the foundation of most building regulations and simulation tools for decades. Sunlight, by contrast, is direct. It casts strong shadows, brings warmth, and delivers a powerful psychological boost that even the most sophisticated LED systems can't replicate.

This distinction matters because most building codes only measure daylight. They ask: "Is there enough light to read?" But they don't ask: "Will this space make people feel alive?"

Historically, building codes focused on daylight for sanitary reasons, ensuring adequate illumination to prevent disease and accidents. Later, the emphasis shifted to energy efficiency and visual comfort. Sunlight rarely featured in standards, except in vague references to "access to natural light." That's beginning to change, but not fast enough and not always in the right direction.

A Dangerous Trade-Off

Gentile warns of a growing disconnect between sustainability frameworks and quality of life. As regulations shift to focus on embodied carbon and lifecycle impact, there's a temptation to view windows and sunlight as liabilities rather than assets.

"Windows can carry a higher carbon footprint than a wall," he told me. "If we focus solely on environmental metrics without balancing social benefits such as mental health, circadian alignment, and cognitive function we risk recommending buildings with less and less daylight and sunlight."

The numbers bear this out. In Sweden, a country once known for its daylight-forward regulations, new codes from July 2025 will remove the minimum daylight requirements for new buildings. This shift, driven by energy calculations, runs counter to decades of research showing sunlight's positive impacts, from mood regulation to property values.

Consider the economic implications: office workers in spaces with adequate sunlight show 15% higher productivity and take 6.5% fewer sick days, according to studies by the Rocky Mountain Institute (Heschong, 2003). A 50,000-square-foot office building could achieve annual productivity gains of $2 million simply by improving its access to sunlight. Yet these benefits rarely appear in lifecycle assessments or building performance metrics.

The Real Cost of Cutting Corners

The consequences of poor sunlight design are becoming visible in our cities. Take London's recent wave of co-living developments, spaces marketed as "wellness-focused" but featuring rooms where residents report feeling constantly tired despite adequate artificial lighting. Or consider the growing number of office retrofits where companies install expensive circadian lighting systems to compensate for blocked sunlight, often at costs exceeding what generous windows would have required.

Healthcare data tells a similar story. Seasonal Affective Disorder rates are rising fastest in cities with the newest, most "efficient" building stock. Hospital patients in sunny rooms recover 8.5% faster and use 22% less pain medication than those in darker spaces, according to research published in Psychosomatic Medicine (Beauchemin & Hays, 1996). Yet hospitals continue to be designed with minimal sunlight access in the name of energy efficiency.

The Data Gap

Part of the problem is a lack of modern data that bridges human experience with building performance. Gentile and Agnieszka Czachura have been working to address this. Czachura's recent survey, based on hundreds of responses across Europe, suggests sunlight is still highly valued, especially for its effect on mood and well-being. But preferences are shifting in response to climate change. Fewer people cite warmth as a benefit, possibly due to growing concerns about rising temperatures and extreme weather events.

Interestingly, when asked to choose between a sunny room with a poor view and a darker room with a great view, two-thirds of respondents chose the view. This suggests that sunlight matters, but so does context. People want both quality light and quality space, a finding that challenges the either/or thinking that dominates current design practice.

Glass Isn't Just Glass

Another issue is that modern glazing technology, in the name of energy performance, filters out not just UV but also infrared radiation. This might make buildings easier to cool, but it also changes the spectrum of light we receive indoors in ways we're only beginning to understand.

Emerging evidence suggests that infrared and UV play crucial roles in everything from eye development to hormonal regulation (Holick, 2007; Turner & Mainster, 2008). Most glass today removes those wavelengths completely. As Gentile puts it: "Daylight indoors is not the same as daylight outdoors anymore."

This spectral filtering may explain why people often feel unsatisfied in spaces with large windows but high-performance glazing. The visual brain receives light, but the circadian system, which relies on specific wavelengths, doesn't get the signals it needs.

Designing for Humans, Not Just Carbon

So what's the answer?

It isn't about abandoning climate goals. It's about rebalancing our definition of performance. European sustainability frameworks already include three pillars: environmental, financial, and social. Yet Gentile argues that in practice, "the social dimension (health, daylight access, view, well-being) is routinely ignored."

Copenhagen's International School, designed by C.F. Møller, achieves Passive House standards while providing every classroom with direct sunlight access through carefully angled facades and internal courtyards (Møller, 2017). 

This example suggests that the trade-off between carbon and comfort isn't inevitable; it's a design challenge that requires more sophisticated thinking about building performance.

Tools for Change

The industry needs better metrics. Current green building standards accurately measure energy use, water consumption, and material embodied carbon, but assess human comfort through crude proxies, such as temperature and illuminance levels.

Gentile and his team at Lund are working with the International Energy Agency and the European Standardization Committee to develop new measurement tools that quantify sunlight quality, not just quantity. These tools would consider factors such as seasonal variation, spectral content, and duration of exposure, creating a more comprehensive picture of what buildings actually deliver to their occupants.

Technology can help, too. Smart glass that selectively filters wavelengths, dynamic shading systems that follow the sun, and building orientation software that optimizes for both solar gain and sunlight access are becoming more sophisticated and cost-effective.

A Call for Integrated Thinking

The path forward requires acknowledging that sustainable buildings must be sustainable for people, not just the planet. This means updating our procurement processes, design standards, and performance metrics to account for human flourishing alongside environmental impact.

For architects, this means designing with sunlight as a primary material, not an afterthought. For developers, it means recognizing that sunlight access drives long-term value through higher rents, lower turnover, and reduced operational costs. For policymakers, it means crafting codes that balance environmental and human performance rather than treating them as competing priorities.

"Buildings are becoming more energy-efficient," Gentile says, "but we have to ensure they remain people-efficient too."

The message is simple but urgent: Sunlight Matters. It's time to design with it, not around it. The cost of getting this wrong isn't just dimmer spaces but dimmer lives, less productive workplaces, and cities that work against human flourishing rather than supporting it.

The buildings we design today will shape how people live and work for decades to come. We possess the tools and knowledge to create spaces that serve both the planet and its people. The question is whether we have the will to use them.

References

• Beauchemin, K. M., & Hays, P. (1996). Sunny hospital rooms expedite recovery from severe and refractory depressions. Journal of Affective Disorders, 40(1-2), 49-51.

• Heschong, L. (2003). Windows and offices: A study of office worker performance and the indoor environment. California Energy Commission.

• Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266-281.

• Møller, C. F. (2017). International School of Copenhagen: Sustainable architecture and learning environments. C.F. Møller Architects.

• Turner, P. L., & Mainster, M. A. (2008). Circadian photoreception: Ageing and the eye's important role in systemic health. British Journal of Ophthalmology, 92(11), 1439-1444.