Olympic Swimming Hall, Munich, Germany. Architects: Frei Otto and Gunther Behnisch, 1972. Photo by Lisa Heschong, 2025.
Talking to Lisa Heschong on an early Thursday morning in March felt like a circadian boost. Her energy, depth of knowledge, and passion for daylight were so engaging that I lost track of time and place. Our conversation about healthy architectural planning explored the many complex dimensions of daylight, ranging from thermal balance and “circadian snacks” offered by a window to the bodily experience of light and the essential role of darkness.
Carlo Volf, PhD
Q: Your work is informed by the conviction that daylight is essential for creating buildings that protect people’s health. Please tell us how you came to that realization.
I grew up in sunny Los Angeles in Southern CA. After obtaining an undergraduate degree in ecology and environmental planning at UC Berkeley, I moved to Boston, for graduate school in architecture at MIT. There I soon had a job working on plans for a proposed housing development to be located in a watershed. We needed to respect its natural environment, including plants, animals and the local microclimate. Based on that experience, I ended up becoming the department’s resident “ecologist” and the teaching assistant for a lab course on microclimatic design.
I soon realized that microclimatic design outdoors was very similar to passive solar design indoors. Also, that when I was using sunlight to help heat a home, I was also creating a daylit environment. I interned at a New Hampshire firm designing solar homes around New England, and became fascinated with the potential for beauty of various passive solar heating systems. For example, we placed large fiberglass tubes filled with water behind south-facing windows.
In addition to storing solar heat very efficiently, they also transformed beams of intense sunlight into a delicate iridescence.
This firm, Total Environmental Action (TEA), also produced “Solar Age Magazine,” one of the early sources of information about solar design and technology. I often helped out with graphics or writing. The best assignment was when I was asked to interview William Lam, the founder of Lam Associates in Boston, a pioneer in daylighting design. I literally sat at his feet and soaked up his love of daylight.
Having moved first from California to Boston, and then to New Hampshire, I was learning how to live comfortably in progressively colder climates. I had also traveled in hot places, like India and Morocco, and was intrigued by how other cultures addressed thermal comfort in their vernacular buildings. All these experiences fed into my Master’s thesis, which became the book Thermal Delight in Architecture.
One of my final projects at TEA was the design of the passive solar “Brookhaven House” for the then newly formed US Department of Energy. Our objective was to design a very modest suburban home which could be easily built (and sold) by any developer in the northeastern United States.
We analyzed a variety of construction strategies and settled on a sequence of handsome brick floors and walls, which provided the thermal storage.
These were set behind standard double-glazed residential window units and a small pre-fab greenhouse, all facing south. One of my favorite design innovations was an ambiguous floor plan, such that the house could be approached from any direction and still present a logical ‘front door.’
This enabled the house to be sited comfortably on a wide variety of lots, even while the solar windows always faced true South. Ultimately, a demonstration house was built on the site of Brookhaven National Laboratory in New York.
The innovative construction of this protype was filmed for an educational video that accompanied construction documents disseminated around the country. The original building was monitored as a laboratory demonstration for a year to verify its extremely energy-efficient performance. Ultimately, a couple hundred of these homes were built in the 1980s.
Unfortunately, in the United States, our energy codes have decided to ignore the benefits of solar orientation.
Instead, they rely almost exclusively upon insulation and limiting window area as the primary mode of energy efficiency, allowing designers to ignore orientation. In a similar vein, the variation in temperature and daylight that are a natural consequence of passive solar design are often at odds with traditional engineering standards that favor uniformity in both space and time.
I, on the other hand, believe that variation is an essential component of human health and comfort. That is certainly one of the key themes of Thermal Delight in Architecture. The sun and climate are dynamic systems, and our body responds with its own dynamic system. It seems logical to me that our buildings, as intermediaries, should also respond with dynamic conditions.
The natural variation of daylight is truly one of its greatest pleasures. However, the electric lighting profession has been trained to design for uniformity, usually with the goal of providing a singular optimum illumination throughout a workplace. Identifying an optimum condition, and then striving to maintain it everywhere, is an engineering mindset, not a biological mindset.
We humans are lucky to have evolved an enormous range of adaptation to illumination levels, by eight or nine orders of magnitude, from starlight and moonlight up to full noon-day sunlight. Daylit spaces indoors can easily experience four logs of daylight illumination over the course of a day, say from 1 to 1000 lux, from bright sun patches to soft ambient illumination. And that variation is not only enjoyable; it helps to keep us healthier and invigorated.
Q: Do you think your perspective applies only regionally (for example, in the U.S), in contrast to other regions (e.g., Denmark)? If so, how? Specifically, how might American buildings differ from those elsewhere?
I think that understanding the local culture and climate is the foundation of good architecture. Without that, you may just have a pretty, but useless, piece of sculpture!
Unfortunately, today in the US, there are very few requirements for daylight in buildings. Back in the 1950s and 1960s, schools in California were reviewed by a state agency for sufficient daylight illumination.
Classrooms of that time were designed with large primary windows facing north, and smaller secondary windows collecting reflected sunlight from the south. However, by the middle of the 1960s these state requirements were dropped.
School buildings got ever bigger and deeper, often combining classrooms for shared teaching. Windows got ever smaller and darker, because it was thought that electrical lighting and mechanical ventilation were adequate.
Some schools even completely eliminated windows, on the theory that they merely created a distraction for the students. By the time I became a registered architect in California, the only remaining building type with requirements for daylight were prisons.
This shift happened at a national level also. In the 1990s, during a process of consolidating three major US building codes, one single word substitution made a world of difference.
In the original sentence “All habitable rooms shall have natural and electrical lighting”, the word “and” was changed to “or.” Now instead it reads: “All rooms shall have natural or electrical lighting”.
I am envious of situations in Europe, such as in Germany, where the labor codes stipulate a certain maximum distance to a window for office workers.
Our codes in the US do not yet recognize access to daylight and sunlight as a basic health need.
To date, daylight is primarily considered an energy issue, with requirements focused first on minimizing heat gain and heat loss, and secondarily minimizing the use of electric lighting where and when sufficient daylight is available.
Unfortunately, our energy codes in California also fail to recognize the advantages of careful solar orientation, or to give credit for operable shading, unless it is automated.
As a consequence, there is a great reliance on the efficiency of mechanical and electrical systems to reduce energy use rather than climatic design. We all know there are good designers who carefully integrate siting, landscape design, and climatic design to make comfortable, healthy, energy efficient buildings.
But these are generally the buildings for wealthy folks who can afford an architect. Cheaper buildings, built to minimum legal standards, are usually simple boxes with little concern for the health or well-being of the occupants.
This tiny change has created a great deal of mischief! Housing developers soon began to assert that windows were no longer required, especially in bedrooms, kitchens and dining rooms.
Q: Tell us about your favorite buildings. How do they reflect evolving concepts about daylight and circadian rhythms?
As a child, I lived outside of Los Angeles, close to The Wayfarer’s Chapel, also known as “The Glass Church.” It was designed in 1950 by Lloyd Wright, the son of Frank Lloyd Wright. It sat on a bluff overlooking the ocean.
Ivy climbed the glass walls and arching cypress trees provided shading to the glass roof.
Triangular framing for the windows and skylights mimicked the natural angle of the cypress branches, merging the chapel with the landscape.
Only later did I learn that the chapel was dedicated to the Theosophist Emanuel Swedenborg, and his philosophy of God being one with Nature.
But as a child I completely understood the message of the design, and asked my mother if we couldn’t please go to that enchanting church.
Just recently I spent a few days at the Ahwahnee Hotel in Yosemite Valley. It was built in 1920s in the Craftsman Style as a grand hotel, with the intent of helping visitors to immerse themselves in the beauty of Yosemite.
This building provides a master class in both thermal and visual delight. Enormous windows are oriented to perfectly frame views of Yosemite’s monumental waterfalls and granite formations, enabling hotel visitors to enjoy them from dawn to dusk.
The hotel features both huge fireplaces to warm evening gatherings, and a grand public solarium, shaped as a half-octagon, where visitors can pass time in warming sunlight at any time of the day or season.
Outdoor patios, sheltered from the rain, face south and east, perfect for morning coffee. Built with local stone and timber, the building offers a seamless transition between the indoor and outdoor environment.
Another master of “designing with nature” was Richard Neutra, an Austrian who became a famous mid-century modern architect in Los Angeles.
I read books about him when I was young, but did not have the opportunity to visit his many buildings in Los Angeles until recently. His writings about “Nature Within” were prescient. He very much wanted to merge healthy living with every aspect of his designs.
He experimented with radiant heating, low-iron glass, and removing boundaries between indoors and outdoors. Huge sliding glass doors led out to sunny patios intermingled with reflecting ponds and shade trees.
His design innovations set the style for the architecture I experienced as a child and which I came to think of as a Californian norm.
An excellent example of a sports hall which takes full advantage of daylight to create a superb setting for exercise is the Olympic Swimming Hall in Munich, Germany.
It was completed in 1972, as part of architect Frei Ottos’ audacious design for an tensile structure to provide shelter across the entire Olympic Park.
The pool’s undulating, semi-transparent roof meets tall window walls, creating layers of gentle luminosity, further reflected in the water’s surface.
The result is a uniformly bright ambient daylight illumination, which together with the views to the landscape beyond, provide a sense of swimming freely outdoors, yet without glare from direct sunlight or concerns about the vagaries of weather. 50+ years since its construction, it remains one of the most beloved sports venues in Munich.
Q: You mentioned the beautiful views from the Glass Chapel and the Ahwahnee Hotel in Yosemite. How do views fit into daylight design?
I like to think about window views as the delicious flavors that motivate us to eat a good meal, and circadian stimulus as the nutrition from the food. Views are what make us want to look out a window more often.
A window view is generally much brighter than the ambient lighting indoors, usually brighter by one if not two orders of magnitude. A view is also much more interesting, which is why people feast their eyes on it.
Glancing out a window can thus provide quick bursts of circadian stimulus, which I call “circadian snacks.” We also know that people are quite tolerant of glare from a window when they find a view interesting.
For example, thousands of homes lining the hills of Berkeley, California have huge west facing windows designed to frame the sunset over the Golden Gate Bridge. And for those few magical moments homeowners put up with hours of glare from the low angle afternoon sun.
I spend a lot of time in my book “Visual Delight in Architecture” analyzing what makes a view attractive.
There seem to be a number of basic elements which are always considered positive: a view of the sky, the horizon and distant landscapes, water features, leafy plants and trees, human and animal activity, interesting architectural details….but it can also be very personal, based on local culture and an individual’s experience. So, my simple summary is: “A good view is one that you like to look at.”
Q: Do you think architecture should account for morning vs evening sunlight (time of day) and summer vs winter sunlight (seasonal contrasts)? How can architecture balance exposure to and protection from sunlight?
Back in the passive solar architecture days of the 1980s, large facades facing south were always considered the best orientation, as they combined the most solar heat with the best opportunity for shading.
North facing windows were second best, with little need for shading, and facades facing east or west were problematic, to be minimized. I have since learned that there can be many advantages to east or west facing windows, if thoughtfully designed.
For example, for many years, my company had offices in a garden-office building with large east and west facing clerestories mounted high in shed roofs.
As I came to work in the morning the east facing clerestories provided a burst of bright light that got the day off to a good start. From mid-morning to mid-afternoon, we had a variety of pleasant views out into the shady garden.
Then came another burst of sunlight into the west-facing clerestories, signaling the end of the day.
The building was designed so that these bursts of low-angle direct sun struck other high walls, and so did not cause visual or thermal discomfort for anyone.
They did, however, create a very pleasurable daily rhythm—shorter in the winter and longer in the summer—but always predictable.
I find that lighting designers are often worried that windows will create glare, especially in offices and other workplaces, via too much contrast with the adjacent interior surfaces.
Their solution is often to add more electric light onto the nearby walls. Instead, I would argue that the best solution to excessive window brightness is usually more daylight, especially more daylight from a second source in the room.
"I am a firm believer that the solution to properly managing sunlight is operable shading systems, controlled by the occupant."
Skylights, clerestories, windows in other walls, can all help to balance the daylight in the room, creating more uniform illumination, both in space and time. Daylight from two directions naturally balances itself throughout the day, rising and falling together with daily and seasonal patterns.
In answer to your other question, I am a firm believer that the solution to properly managing sunlight is operable shading systems, controlled by the occupant.
We should certainly design exterior shading systems and plant appropriate vegetation to help manage the seasonal vicissitudes of sunlight. However, inevitably there will be stray reflections of sunlight— off of a car window, a rain puddle, an adjacent building’s window—which can cause extreme visual discomfort.
Such reflections are almost impossible to predict; thus the need for operable window shading systems that can be quickly deployed when needed. If the view is nice enough, if the operating system is easy enough, and if occupants feel they have enough privacy and autonomy, I think there is a very good chance the occupants will open the blinds or curtains once the problem has passed.
Automated systems can also provide a default open condition that occupants can choose to override for a pre-set time condition, such as an hour or two. But we have found that automated systems that also try to anticipate glare problems are generally judged annoying, and are disliked by occupants.
Q: Do you think we have forgotten something from the past when we design buildings today? If so, why would we forget or disregard such cumulative wisdom? (And what can we do about it?)
Daylight is, in its very essence, a bodily experience. There is a lot to be learned from simply spending time in a well-daylit building. People are rarely conscious of the daylighting quality of a space; but once it has been pointed out to them, they can’t stop looking.
So a little bit of education, combined with a lot of physical experience, is probably the best way to learn how to design with daylight.
A lot of vernacular and classical architecture was based on the same principles and rules which still apply today. So there are many convenient examples to study. Meanwhile, our knowledge about the biology of light and circadian physiology is rapidly advancing. We are learning more details about the underlying biological mechanisms.
At the moment, keeping up with all these advances in light and health could be a full-time job. Currently, lots of people only know one piece of the puzzle.
As some folks like to say “The future is already here. It is just poorly distributed.” I predict that there will soon be a second revolution in light and health, whereby it will become widely understood how utterly essential daylight is to human health.
Thus, I prefer an architecture that fundamentally responds to climate and biology, not to fashion.
Climate and biology don’t change with fashion. Being in a garden is just as wonderful today as it was 50 years ago, or 500 years ago for that matter. The physics of light doesn’t change.
Our physiological response to light does not change. We can, however, endeavor to understand it better. Architects and designers should learn to work with nature—both the nature of our bodies and the nature of the environment. That is our canvas, what we are working with—doing anything less to me simply seems silly.
Architecture is the grammar of our lives. It creates structures for what is physically possible and what is not possible in our daily existence.
Offering the beauty of daylight throughout our buildings would seem to be one of the greatest gifts an architect can offer to people of the future, those who will inhabit our current buildings for generations to come.
Designing an energy efficient building, a healthy building, an economical building, a safe building, should always be a basic starting point.
But the end point should always be an environment that is also joyously beautiful: the delight of daylight.
Lisa Heschong FIES, the 2022-2023 IES Medalist, has been researching, writing and speaking about lighting efficiency, daylight, and human health for most of her long career. As an architect, she designed daylit buildings. Then as a founding principal of the Heschong Mahone Group, an energy consulting firm, she helped develop many of the lighting provisions in California’s Title 24 and taught Federal energy managers about energy efficient lighting retrofits for over a decade.
She also led groundbreaking research finding an association between more interior daylight and window views with increased retail sales, cognitive performance in office workers, and student test scores. As chair of the IES Daylighting Metrics Committee, she led the effort to establish spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE) as the current IES/ANSI standard for climate-based daylight performance. Most recently, she authored “Visual Delight in Architecture: Daylight, Vision and View” and has been collaborating with scientists around the world on the intersection between daylight and public health.
