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In recent years daylighting was most often discussed, in lighting circles, as an energy issue, and included in codes as such. Today, wellbeing and human-centric lighting are trending, recalling “right to light” statutes of the nineteenth century when the industrial revolution ran on coal and daylight. Advancements in glass and automation, human research, daylighting metrics and computer modeling underlie a renewed appreciation for the ability of daylighting to enhance the human experience in architecture.

The inclusion of health and wellbeing measures in standards like LEED and the Living Building Challenge have added a dimension to sustainable buildings that daylighting suits perfectly. Circadian effects of electric lighting are a hot topic, but electric lighting pales in comparison to the timing, power, and spectral distribution of daylighting; and that’s in addition to views and connection to the outdoors. New research upholds the restorative effects of view and is currently exposing benefits in sleep and alertness, Vitamin D synthesis and a decrease in indoor bacteria.

Photo by Amir Nezamdoost of closed blinds.
When manually operated, once blinds are closed, they tend to stay closed. This makes a good argument for automation to retain daylight harvesting and access to views.

Glare and solar heat gain are the primary thorns in daylighting designs, particularly in today’s computer-intensive work spaces. Different codes require internal or external shading to ensure workers’ comfort and protect from disabling direct-sun glare. Other types of daylighting glare, however, are a function of task direction and adaptation (Is the glare source extremely bright compared to the surrounding visual field?), which can be tricky to anticipate.

Dynamic shading solutions like manual or automated blinds or shades remain ideal, as they can be effective in a transient glare situation but can be readjusted to allow skylight and views during most of the occupied hours and on cloudy days. “Hopefully you’ve done a good passive design, and [direct sun glare is] short in duration and relatively infrequent. But even then you’re probably going to have some periods of time when you’re going to need some modifying element,” said Kevin Van Den Wymelenberg, director of the Energy Studies in Buildings Laboratory (ESBL) at the University of Oregon.

“I’m on record as being a proponent of various forms of automation. There’s several frontrunners right now. The automated lines of one shade or another – rollers and louver fabrics – and then there’s also dynamic glazing: electrochromic, thermochromic, and others.” Van Den Wymelenberg favors automation because once a blind is closed it can be left closed. Even an automated end-of-day reset to open blinds can be advantageous. The next step is “smart windows” combined with sensors to track the sun and respond to weather conditions, integrated with a whole-building controls network or IoT. “There’s also really exciting opportunities for automation to tune over time with machine learning algorithms to people’s preferences,” he said. A different tack is personal, adjustable shading devices, perhaps integrated in furnishings.

Photo by Jeff Ozvold of daylighting in and atria.
Though their contribution to adjoining workspaces is small, biologically powerful levels of daylighting and views can be enjoyed in transient spaces like atria, cafes, lobbies, etc.

Access to daylight and views has been studied in all sorts of spaces – hospitals, schools, retail, etc. – and found beneficial. Often tasks or building orientation prevent broad fenestration, but direct sun is readily tolerated in entrances, breakrooms and other transient spaces. For instance, “the number one goal of an atrium could just be to have a space in the building to go and have access to light. The basic ‘light for everyone’ idea actually goes back to the right to light,” Van Den Wymelenberg explained.

Right to light is a type of easement that encumbers property owners from blocking their neighbors’ daylighting or views.

When the access and use of light to and for an dwelling-house, workshop, or other building, shall have been actually enjoyed therewith for the full period of twenty years, without interruption, the right thereto shall be deemed absolute and indefeasible, any local usage or custom to the contrary notwithstanding.
The Prescription Act of 1832 (UK)
Photo by Wally Gobetz of stepped architecture with daylight laws.
Stepped architecture in conformance with “daylight” laws is evident at the American Radiator Building in NYC, opened in 1924.

Such regulations, court cases and workarounds have certainly shaped metropolitan skylines throughout the twentieth century, and today. Where human-centric lighting is incorporated into code language (look to Europe), access to daylight and view is being defined and mandated.

The energy argument

Is energy conservation still a driver? “Five years ago if you had asked me that question I would have prioritized health, energy efficiency, then productivity. I still think that those three buckets are reasonable, but I’ve spent a lot more time in the last few years looking at health than I have energy or productivity,” said Van Den Wymelenberg. “I think energy is still a big piece of the equation, but even 10 or 15 years ago, the longer lever arm was always health and productivity, occupant satisfaction and recruitment and retention.” He added that the use of renewables and net-zero building has changed the grid’s load shape (photovoltaic power is plentiful when the sun shines), but the increased use of batteries may spur more daylighting-for-energy-efficiency measures in the future.

Galen Burrell, senior daylighting specialist with View Inc., agrees: “There’s still a story for daylight with regards to energy, but it’s just not the most compelling one. I think by far the most compelling narrative around daylight is occupant comfort, occupant happiness and wellbeing.” He conceded that there can be a huge difference between energy savings modeled and what is realized in the occupied building. “It depends on occupant behavior and how well the building was commissioned…. There’s a lot of places were that can sort of fall apart.” Comfort and wellbeing aspects can likewise be affected.

Even with highly efficient LED installations, George Loisos, principal and coowner at Loisos + Ubbelohde, still sees large energy savings with passive daylighting: “For something like an office or an institutional building, it can have enormous effect. We’ve had situations where we’ve reduced energy use by more than 50% by doing good daylighting design.”

Improvements in window technologies continue to advance. Super-efficient, microlouvered and electrochromic glass are all expanding in use. Spectrally selective, low-e glazing offers plentiful daylighting with minimal solar heat gain and has become standard.

In-situ HDR photography is helping to improve glare metrics and validate computer-modeling algorithms
Evolving metrics

Burrell described an “inherent tension” between maximizing daylight and risk of glare. The LEED daylighting credit considers daylight autonomy (DA) [related to useful daylight illuminance (UDI)], which is the percentage of occupied time that horizontal illuminance needs are met by daylight, without overlighting. LEED also uses a glare/thermal comfort metric: annual sun exposure (ASE) describes the portion of the space receiving too much direct sun (>1000 lx for 250 occupied hours) to be comfortable.

Daylight glare probability (DGP) and daylight glare index (DGI) express good-bad-intolerable subjective assessments of brightnesses in the heads-up field of view, based on the position of glare sources and contrast. These metrics have been used in daylight modeling software and compared in-situ with HDR photography (which processes images as “multiple exposures”), producing only limited validation of the metrics. “I’ve looked at spaces that if you do the calculations, they come in at painfully horrible and they look great to me. So it’s how you use it and where it’s used,” commented Loisos. “The definition of what glare is, and where glare is a problem, is in flux.”

Burrell disagreed here: “Between those two metrics, daylight glare probability and daylight autonomy, you can usually come up with a pretty good understanding of A. how much daylight you are introducing, and B. how well you are addressing visual comfort in the space.” Glare metrics and their use in simulations continue to be tested and refined.

This is partly why no-brainer passive daylighting designs don’t get built: “This stuff is, on the one hand, very complicated to measure, very complicated to define; and then extraordinarily complicated to actually build. So we cut corners on all of them,” Loisos said. He still works hands-on with new architectural materials to see how daylight behaves and builds scale models to understand and communicate daylighting strategies.

At Valley Children’s Medical Group, Loisos + Ubbelohde modeled several diffusion strategies to reduce sky brightness and for thermal and visual comfort. They settled on a combination of graduated frit on the curtain wall and tensile “kite” shades that add visual interest.

Simulations: increasing complexity

Though they are time-consuming, computer models are a mainstay: “They’re much better at predicting performance, and our confidence has increased in them a lot. But that has come at a huge cost.” Loisos explained that training is expensive. “The number of variables that are in the software are a lot, and knowing which one effects which… The problem is that you can get a perfectly reasonable answer that is wrong, and you’d never know…. The experience that is required in order to do [error-checking] well is substantial.” Cloud computing has allowed more complexity and increased numbers of simulations, faster, but also at a cost.

Photo by Benjamin Benschneider of daylighting from multiple sides.
Daylighting from multiple sides – a tried-and-true strategy for visual comfort – is seen here at the uber-efficient Bullitt Center in Seattle.

“The place where a number of simulations, rather than doing one, helps is because you start seeing the differences between different lighting conditions, and you can start applying your judgment on that. This is where a single number is not terribly useful,” Loisos said. Heads-up computer work is a difficult visual task and sun and sky conditions change seasonally and daily. “Being able to predict how [people can] work under different conditions takes quite a bit of experience. And we can’t possibly do simulations of every possible configuration and design option because that would be close to infinite. We have to be able to think on our feet; do a number of simulations; and then direct the design team towards one solution rather than another. Working in real-time you don’t have a lot of time to do this. Sometimes we have days or a week to compare these analyses.”

Effective daylighting is complex, but common rules of thumb include light from multiple sides, diffuse skylights, tall windows and a narrow floor plate. Van Den Wymelenberg emphasized setting daylighting goals early on. But still, Loisos warned, interesting and effective daylighting designs often fail to survive value engineering. But this may be turning around. “By providing a well-designed daylighting system – the more you try to play to those occupant benefits, the better chance you have of achieving successful outcomes in terms of those intangibles,” Burrell added.

Incorporating daylighting in the conceptual design of buildings (orientation, envelope, windows and shading, etc.) can enhance affection, according to Loisos. “It could make the difference between a building that is incredibly successful and works fantastic, and a building that’s just a building. It’s not loved, and it’s not appreciated. In our minds here, we think of that being a particular sustainable aspect of a building. Because a building that has affection to it is likely to be around much longer than one that doesn’t.”

Lois I. Hutchinson

About Lois I. Hutchinson

Lois I. Hutchinson is a freelance writer specializing in lighting and energy issues. She is also the content marketing mastermind behind Inverse Square LLC, a Los Angeles–based consultancy. Contact her via with your comments and any article ideas that concern the lighting community here in the Southwest.

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