The light we see is as important to our health as the air we breathe, the food we eat, and the water we drink. THE LIGHT DOCTOR shows you how to take charge of the light you see and avoid using harmful and unhealthy LED and fluorescent light.
Chapter 6 discusses the challenges of illuminating our buildings with natural daylight. It used to be the only option, but we got lazy with the invention of electric light.
The indiscriminate use of electric light has got us in trouble, and now we need to be creative in finding solutions to the health crises that we have created. The global lighting industry has grown into a $130 billion a year behemoth
by focusing almost solely on illumination aesthetics and energy efficiency at the lowest cost. As I will discuss in the next few chapters of THE LIGHT DOCTOR, effective healthy lighting solutions are now available, but it will take consumer insistence – this means you – and maybe regulatory warning labels, to turn this massive lighting industry around.
Before electric light most people spent their days outside exposed to blue-rich daylight.
In the old days, before electric light was conceived, our ancestors spent much more of their time outdoors exposed to the health-giving rays of the sun, and when they were indoors their architecture was designed to let in natural blue-rich daylight. Then after the sun had set, fires and candles emitting virtually no blue light were used to extend the wakeful day before they retired to sleep. These were the conditions that were recreated in the Rocky Mountain camping trips that we discussed in Chapter 2: Goodbye Milky Way, where the campers’ circadian rhythms and sleep patterns became robust and healthy under the high-blue day, low-blue night, lighting conditions of the pre-electric natural world
Fundamentally there are three solutions for ensuring circadian health:
1. Spend more time outside – especially in the mornings at a regular time
2. Bring daylight indoors – which has its limitations, as we will discuss in the chapter, and
3. Redesign electric light to provide blue-rich days and blue-free nights - which is addressed in the next three chapters.
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How Much Time Should We Spend Outside?
Outdoor exposure to natural daylight provides the greatest boost to our health. People who spend sufficient time outside each day, sleep better and longer at night, and are healthier. Most important is the exposure to bright blue-rich daylight in the morning hours before the sun is high in the sky. This is when daylight is most effective at synchronizing our internal clocks and preventing the drifting apart of our circadian rhythms.
SCIENTIFIC ASIDE: What is Daylight?
Daylight is a dynamic and complex mixture of direct sunlight, scattered light from the sky and reflected light from nearby vegetation and buildings.
Scattering occurs when small particles and molecules in our atmosphere preferentially absorb and then scatter blue light photons in the Rayleigh effect, accounting for the blue skies on a sunny day, as we discussed in Chapter 3: Clockwork Blue. In contrast all the visible wavelengths of sunlight entering clouds are equally scattered in all directions by water droplets greater than 20 micrometers in size (called Mie scattering
) so that the clouds emit full spectrum light, and therefore appear white. The underside of clouds appears dark only when they are too deep, or too dense with water droplets, to let sunlight through..
Much of the light that reaches the earth, either as direct sunlight or scattered light from the sky, is reflected off trees and other vegetation, and buildings and other objects in our landscape before it reaches us. The colors we see depend on which light wavelength photons are absorbed by the object and which are reflected. So, because the leaves of plants and trees contain chloroplasts they absorb blue and orange-red light to photosynthesize sugar nutrients, but reflect the green photons. This is why the leaves appear green, and the reflected light from vegetation is relatively richer in green wavelengths.
Daylight is dynamic because the sun is constantly moving across the sky, or more accurately our sky is moving across our sun. As it moves this alters the amount, direction and type of light scattering and light reflection. Add to that the weather conditions that are ever changing. The result is a dynamic daylight experience, that our ever-constant electric light does not replicate.
Today less than 2% of the population of the developed world works outdoors. Unless you are a farmer, forester, or landscape gardener, it takes effort to find the time to spend outdoors. Before the industrial revolution, and in the underdeveloped world today, 70-80% of the population worked on the land. Given there is no way most of us want to go back to that outdoor life, what is the minimum amount of daylight we really need?
A study of 593 people working at home during the CoVid epidemic showed that significant benefits were gained when people spent 1-2 hours outside in natural daylight each day. Thirty minutes was not enough, but once they spent 60 minutes or more outside, sleep quality and alertness were improved, and anxiety and depression were reduced
Other studies have shown a reduction in body weight in people who are exposed to natural outdoor light. Body fat levels are reduced by the simple exposure to bright daylight in the mornings
. This speaks to the fundamental effects on our metabolism when our circadian clocks are properly aligned, and our circadian rhythms made more robust.
Ideally you would get outside and expose yourself to daylight within an hour after dawn or within an hour after waking whichever comes later. This timing provides the maximum light resetting signal to the circadian clock, but avoids truncating your sleep and making you unnecessarily sleep deprived. As you find light having its beneficial effects, the morning light exposure will gradually move your waking time earlier.
But life is complex, and the demands on your time are many, so at the least the outdoor light exposure should be every morning, as early as is practical.
Bringing Daylight Inside
If you cannot get outside because of inclement weather, conflicting commitments or infirmity, the second-best option is to bring the daylight inside. There are two major problems with bringing daylight indoors. First, on a sunny day if the window is facing east, south or west there will be a time of day when the beams of sunlight may be too bright and cause glare. That can be handled using shades or louvers. A bigger problem is the brightness of daylight diminishes rapidly the further you get from a window. This phenomenon called the “inverse square law of light” greatly limits the usefulness of daylight within buildings.
SCIENTIFIC ASIDE: Inverse Square Law of Light
Inverse Square Law of Light. Reproduced with permission of elixxier Software GmbH www.elixxier.com
The easiest way to explain the inverse square law of light is to consider a room with a one-meter square window (approximately 3 feet 3 inches x 3 feet 3 inches). The photons of daylight that enter that window come from multiple different directions, and spread out as they cross the room. The farther they travel across the room the same number of photons are illuminating an increasingly larger area, and therefore the brightness measured in photons per square meter per second progressively falls. One meter from the window the photons will illuminate an area four times greater than the window (2 meters x 2 meters), and the light intensity drops to 25% of that measured at the window. Two meters from the window the photons are spread out over an area nine times larger than the window (3 meters by 3 meters) and the light intensity drops to 11%, and three meters from the window the area covered is sixteen times larger (4 meters by 4 meters) and the light intensity is reduced to about 6% of the original. In mathematical terms this law can be expressed as the light intensity is reduced by the inverse square of the distance from the light source, and this is true for any light source including windows, light bulbs and fixtures.
This is the definition of the inverse square law you will find in physics textbooks or on the internet. It is technically correct, but it is not what happens in the real world. The inverse square law only applies to unrestricted space where there are no reflecting surfaces. If some of the photons of light from the window or lamp are reflected off other surfaces, such as floors, walls and ceilings, this will add to the total illumination you receive, and significantly reduce the effect of the inverse square law.
To demonstrate this, I visited one of the spectacular new buildings with huge picture windows on the Boston waterfront, the St Regis Residences
, which offer condos with breathtaking views. Would the light coming in through those windows drop off with the square of the distance from the window?
Measurements of illumination at the north-facing windows and 4 meters from the windows of the St Regis Residences on the Boston waterfront demonstrating that light penetrates farther than is predicted by the inverse square law of light.
To avoid the complications from beams of sunlight I asked to see a north-facing unit at noon with the electric lights all switched off. First, I measured the light coming in from the window with my spectrophotometer pressed against the glass. It was only 2,266 lux, far below the 9,500 lux I measured facing north outdoors. The difference was due to the light absorbing window glass which appeared to have had a Visible Light Transmission (VLT) of about 24%.
Then I measured 4 meters back from the window where the Inverse Square Law would predict the illumination would fall to 6.25% of the window measurement which would be 142 lux. Instead, my spectrophotometer measured 897 lux, which meant that the illumination at 4 meters away was only 40% less than the window measurement. The reason was that the reflection of window light, off the white walls and ceiling and the floor, redirected a lot of additional light photons towards my eyes and the spectrophotometer. Distance from the window is still an issue in interior daylighting, but less than that predicted by the Inverse Square Law.
Pre-Electric Architecture
“The history of architecture is the history of the struggle for light” as Le Corbusier, the revolutionary architect wrote in 1927
. Before electric light, every building had to rely on natural light during the day since candles, oil lamps and fires were impractical and too expensive to be used all day long. It was a constant struggle to balance the excessive glare from beams of direct sunlight on sunny days, with the challenge that the brightness of light diminished rapidly on cloudy days the further you stood from a window.
In the pre-electric era, most of the population spent their days outdoors and only returned to their homes at night. So, daylighting the home was not an issue and windows were better kept small to exclude the rain and snow, and reduce the loss of heat in winter. For people who did spend their days indoors, windows had to be large and building interiors narrow, or built with internal atriums and courtyards so that their occupants were never too far from the daylight entering a window.
The ancient Pantheon built in Rome in 127 AD is illuminated by an circular opening in the roof called the oculus.
Larger public gathering spaces, such as temples and cathedrals, used skylights or “clerestory” windows high above the surrounding roof tops, to bring in the daylight
. A classic example is the Pantheon, the ancient temple built in Rome in 127 AD, which is still standing and in use today. This circular building 142 feet across is topped by an enormous dome with a 27-foot (8.3 meter) opening, in its center called the “oculus”. On a sunny day a circular sunbeam moves around the interior space marking the time of the day. On a cloudy day a dimmer more diffuse daylight fills the space
Skylights and high windows only work well in single story buildings, or buildings with central atriums providing daylight to several floors. When New York and Chicago started to build skyscrapers of increasing height in the 1870’s, it was recognized by architects that space more than 20 - 25 feet away from a window would be difficult or impossible to rent
. These early skyscrapers were narrow buildings so that the amount of space illuminated by natural light was maximized. Ceilings were high on each floor and windows were tall to bring in more daylight
. Most of these buildings were 15 stories or less in height and have since been demolished and replaced by even taller skyscrapers, but the Flatiron building in Manhattan remains as an example of a building designed before the widespread use of electric light. Except for a small inner core, all the rooms are illuminated by natural light.
The Flatiron building in New York which was built to maximize the use of daylight by having all interior space illuminated by tall windows, except for a small interior core.
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Electric Light in Deep Space
The introduction of fluorescent lights and air conditioning in the 1950’s ushered in the era of “deep-plan” buildings, which freed up architects from relying on daylight for illumination, and windows for ventilation. Construction costs were reduced by greatly increasing the amount of floor space within a set of outer walls, and using electric light to illuminate that interior space.
The executives and senior managers got the windowed offices on the perimeter, but most of the workforce found themselves in windowless cubicle farms under twilight levels of electrical illumination. When the oil embargos of the 1970’s raised concerns about the accelerating cost of energy, building owners responded by dimming electric lights to save on the utility bill
. The math seemed simple. If you could replace 300 lux of light with fixtures providing 100 lux, the electric bill for lighting would be reduced by two-thirds.
This astonishingly short-sighted de-lamping of the workplace caused increased drowsiness and decreased alertness on the job, depressed mood and reduced performance and loss of productivity. In one study conducted in 2020 the benefit of windowed offices with plenty of blue-rich daylight boosted cognitive performance on decision making tasks by 42% as compared to offices with blinds blocking the windows
. The costs of employee productivity loss in the windowless offices thus far exceeded any savings obtained on the electric utility bill.
Venturing too far into Deep Space
The height of ignorance about the value of daylight was displayed when Charles T Munger, a billionaire investor and Berkshire Hathaway executive proposed in 2021 to donate a self-designed dormitory for students at the University of California, Santa Barbara. Munger Hall was designed to house 4,500 students in windowless bedrooms in the interior of a huge 1.7-million-square-foot, 11-story building
The proposed design and floor plan of Munger Hall with 4.500 windowless bedrooms at the University of California, Santa Barbara Archived at https://perma.cc/T87A-2XXS
After the project was announced there was an enormous pushback, with the building being called “a giant windowless prison” and “a recipe for student depression”. The UC Santa Barbara’s architectural consultant, Dennis McFadden, resigned in protest saying “an ample body of documented evidence shows that interior environments with access to natural light, air, and views to nature improve both the physical and mental well-being of the occupants.” Finally in 2023 the mounting criticism led the university to cancel the project and return the $200 million donation to Charles Munger
, “It is the unqualified result of all my experience with the sick, that second only to their need of fresh air is their need of light; that, after a closed room, what hurts them most is a dark room.” Being close to the window and exposed to daylight speeds the recovery of hospital patients and boosts the health of office workers. Employees in windowed offices exposed to an average of 1,000 lux of daylight get 45 minutes extra sleep per night as compared to workers in windowless offices exposed to 390 lux of electric light
. The timing of the daylight also matters. Depressed patients admitted to hospital rooms facing south-east, where they get plentiful morning light, are discharged twice as quickly as those admitted to north-west facing rooms with no morning sunlight
Most regulatory initiatives about daylighting have been concerned with saving energy by dimming electric lights or switching them off when there is adequate daylight from windows. For example, California Title 24 requires electric fixtures near windows to be equipped with automatic dimmers when daylight from windows is bright
But now finally, there is some momentum towards recognizing the health benefits of sunlight. After ten years of drafting, the European Union published in 2018 the European Standard for Daylighting EN 17037, which defines the quantity and quality of natural daylight that occupants should experience
. According to this standard daylight should provide a minimum of 300 lux over 50% of the building space for more than half the daylight hours in the year without using artificial lighting.
Piping in Daylight
A lot of engineering ingenuity is being applied to how to get daylight deep into buildings, especially in the tropics where sunlight is plentiful and electric supply unreliable
. By the use of outdoor light collectors, equipped with mirrors or other reflecting sources to focus and concentrate the light beam, and light pipes or fiber optic cables, sunlight can be transported deep into interior spaces
. These systems can work well during daytime hours on a sunny day, but have to cope with the constantly moving position of the sun, and the impact of cloudy weather where light levels can fall by 90% or more. So, these systems have to be supplemented by electric light.
Illumination Not Adequately Blue
Outdoors during the daytime, in virtually any weather, there is sufficient light of every visible wavelength, including the blue photons which are so essential for synchronizing and strengthening our circadian rhythms. But indoors where light levels are more than 100 times less, we need to pay attention to the blue content of light. Light which is perfectly adequate for vision and performing our daily activities may not contain enough blue to be healthy during the daytime hours, and often has far too much blue content at night.
So efficient are our eyes that we can adapt our vision to a wide variety of lighting conditions, and barely notice the change. We can see our surroundings sufficiently to navigate safely over a million-fold range from less than 0.1 lux of moonlight to 100,000 lux of sunlight, and adapt well enough from one condition to another within minutes. However, we cannot easily judge how much circadian blue light we are receiving.
SCIENTIFIC ASIDE: Flexible Vision is a Priority
We achieve this enormous flexibility in vision by using two systems. First, by automatically varying the diameter of our pupils, depending on the brightness of the light falling on our eyes, the amount of light entering the eye can be reduced or increased by up to 16-fold
. In dim light the pupil is fully dilated letting in as many photons as possible. But as the brightness of light increases the pupil is progressively constricted, reducing the number of photons that would otherwise enter. Under normal conditions, this pupil reflex is most sensitive to green light at about 540nm
, but not to optimize the blue light we need to keep our circadian clocks in sync.
The second system utilizes two types of photoreceptors in our eyes that enable us to see the world around us. The rods in our retina are optimized for seeing under dim light and the cones are designed for optimal vision when the light is bright.
But these two visual systems are not tuned to optimize the circadian blue photons that are detected by the ipRGC melanopic receptors that synchronize our circadian clocks.
Survival of the fittest clearly favored the immediate advantages of optimizing our vision over the longer-term advantage of optimizing our health by keeping our circadian clocks in sync. Without that emphasis on maximizing vision, our ancestors would more easily fall victim to the Sabre tooth tigers and other predators in their world, and would miss opportunities to catch and gather food for themselves. Fortunately, there is enormous redundancy in our circadian daylight-moonlight blue-wavelength detecting system because the contrast in the brightness of light between natural day and night is so great. It was only when we began spending over 90% of our time indoors under twilight conditions that the design of our circadian system has shown its limitations.
We have chosen to live indoors under a constant electrical twilight that is far from the natural cycle of blue-rich days and blue depleted nights. The use of electric lighting confers enormous advantages of convenience and flexibility, but we can only afford this luxury if we make sure we are still receiving the blue-rich day, no-blue night, signal that our circadian clocks require to preserve our health.
You have learned in this chapter:
1. Getting outside and being exposed to natural blue-rich daylight for an hour each day, especially during the morning hours provides major benefits for your health and well-being
2. It is difficult to get sufficient natural light within buildings to improve your health unless you are close to a window because the intensity of indoor light falls rapidly the farther you are from a window.
3. We can see the world around us under a wide range of lighting levels, but our vision does not permit us to be consciously aware of how much blue light we are receiving.
THE LIGHT DOCTOR is a reader-supported publication. To support our important educational mission and receive full access to this book and its references and supporting materials please consider becoming a paid subscriber for no more than you would pay in a bookstore.
Preview of next post: Chapter 7: Tuning to the Right Wavelength.
Just as you have to adjust the setting to your favorite FM or AM channel on your radio to get a clear signal, you have to tune in to the correct circadian blue wavelengths with the electric lights in your home in order to get a clear day-night signal. So, to design electric lights that meet the challenging indoor conditions of being 100 times dimmer during the day and 100 times brighter at night, compared with natural light, we needed to define the precise wavelengths that convey the circadian message. The first scientists to tackle this challenge used dark-adapted volunteers in a darkened room and reported that a broad range of violet, blue, and green light conveyed the circadian signal. But if you remove all violet, blue, and green from the white light spectrum you create a ghastly yellow-orange color that is also quite depressing and unsuitable for illuminating our lives. When we repeated these studies in light-adapted people under regular workplace lighting conditions, we discovered the good news that the circadian sensitivity is confined to a much narrower band of only sky-blue light. This breakthrough has enabled the creation of attractive white circadian light which is either rich in blue for daytime use or devoid of circadian blue for nighttime use.
Schedule
I release a new chapter of THE LIGHT DOCTOR every two weeks by email to my subscribers. The email version will not contain any url reference links, as that can trigger spam filters. The version of the chapter with full references and footnotes will then be uploaded to the Substack website within a week.
I also release a podcast version of each chapter in two parts within a few days after the emailed text version.
I look forward to your comments. There is much to discuss!
Lockwood, D.J. (2016). Rayleigh and Mie Scattering. In: Luo, M.R. (eds) Encyclopedia of Color Science and Technology. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-8071-7_218
Jarbow C and Figueiro M. (2023) More Daylight = More Sleep, Designing Lighting. https://issuu.com/designinglighting/docs/designing_lighting_inaugural_edition/s/10913761 Archived at https://perma.cc/BQW9-JQME
Reid KJ, Santostasi G, Baron KG, Wilson J, Kang J, et al. (2014) Timing and Intensity of Light Correlate with Body Weight in Adults. PLOS ONE 9(4): e92251. https://doi.org/10.1371/journal.pone.0092251
Almodovar-Melendo JM. (2018) Lighting Features in Historical Buildings: Scientific Analysis of the Church of Saint Louis of the Frenchmen in Sevilla. Sustainability 10: 3352; doi:10.3390/su10093352
Hannah R. and Magli G. (2011)The role of the sun in the Pantheon’s design and meaning. Numen 58: 486–513. https://arxiv.org/vc/arxiv/papers/0910/0910.0128v1.pdf
Boubekri M. et al (2020) The Impact of Optimized Daylight and Views on the Sleep Duration and Cognitive Performance of Office Workers. Int. J. Environ. Res. Public Health 2020, 17, 3219; doi:10.3390/ijerph17093219
Keskeys P (2021) Think Architects Don’t Matter? Check out the World’s Most Hated Floor Plan. Architizer Weekly Newsletter https://architizer.com/blog/inspiration/stories/worlds-most-hated-floor-plan-munger-hall/ Archived at https://perma.cc/T87A-2XXS
Boubekri M. et al (2014) Impact of Windows and Daylight Exposure on Overall Health and Sleep Quality of Office Workers: A Case-Control Pilot Study. J. Clin. Sleep Med. 10: 603-611.
Gbyl K et al (2016) Depressed Patients Hospitalized in Southeast-Facing Rooms Are Discharged Earlier than Patients in Northwest-Facing Rooms. Neuropsychobiology 74:193–201. DOI: 10.1159/000477249
Benedetti F. et al (2001) Morning sunlight reduces length of hospitalization in bipolar depression. Journal of Affective Disorders 62: 221–223
National Institutes of Health (2019) Daylighting – European Standard EN 17037. Technical News Bulletin 93. https://orf.od.nih.gov/TechnicalResources/Documents/Technical%20Bulletins/19TB/Daylighting%20%E2%80%93%20European%20Standard%20EN%2017037%20October%202019-Technical%20Bulletin_508.pdf Archived at https://perma.cc/93AC-4UDT
Šprah N and Kosir M (2019) Daylight Provision Requirements According to EN17037 as a Restriction for Sustainable Urban Planning of Residential Developments. Sustainability 2020, 12, 315; doi:10.3390/su12010315
Roshan M. and Barou S. (2016) Assessing Anidolic Daylighting System for efficient daylight in open plan office in the tropics. Journal of Building Engineering 8: 58-69 https://doi.org/10.1016/j.jobe.2016.07.002
Zauner J, Plischke H, Strasburger H (2022) Spectral dependency of the human pupillary light reflex. Influences of pre-adaptation and chronotype. PLoS ONE 17(1): e0253030. https://doi.org/10.1371/journal.pone.0253030
THE LIGHT DOCTOR 6: Bringing the Outside Indoors
Very thorough post about daylighting! I especially loved the history section in the middle. Thank you, Dr!