Metrics that Matter, Part 2 – Visual Comfort and Daylight

Visual Comfort and Daylight Autonomy are two important MEasures of Building Performance and DEsign

Visual Comfort and Daylight Autonomy are two important MEasures of Building Performance and DEsign

The metrics I discuss in this blog series help us make better buildings not only after they’re built, when doing retrofit projects or correcting unfortunate deficiencies in architecture, but at the early stages of design for new building projects, when the important decisions are made. They can help to shape how we design- architects, engineers, and owners typically don’t start a building design with questions like “will people be comfortable thermally in the space?” or “how can we provide excellent light in this building? In early design phases they’re concerned with things like finance, compliance parameters, aesthetics, systems, energy and water use, and above all cost modeling and navigating the inevitable VE obstacle course- pretty much everything BUT the comfort, health, and productivity of the people who will live and/or work in the building. Lighting and HVAC are usually considered after siting and massing are done, structural system chosen, façade designs are approved by the city architectural review board, program completed, and schematic design locked in. To propose new metrics for human comfort and quality in buildings is to ask “what if we started the design process with thermal and visual comfort as primary design considerations?” It may seem simple or obvious, but this approach is almost the opposite of how we practice architecture today.

Visual Comfort
There is no real standard for visual comfort in buildings, and the term is rarely used by design professionals. The Illuminating Engineering Society ( of which I am an active member ) last defined lighting comfort in 1966, with a method that exemplifies the “engineered” approach to lighting, which is not particularly useful for designing real spaces for real people. By default, visual comfort is often defined by its absence- in spaces that are overlit or underlit, or have lighting with poor color rendering, glare, or poor controls. This applies to electric lighting or daylighting and various combinations thereof.

Like thermal comfort, visual comfort is a result of a number of factors that work interactively and can’t really be separated out and measured separately. Broadly speaking, these are brightness, glare, color, color rendering, direction, contrast, and controllability. ( Lighting geeks have other terms for these qualities, like luminance, illuminance, lux, etc., but these are used mostly within the tribe, so to speak ). Many people feel that visual comfort is too “subjective” and difficult to measure, that it’s like trying to measure art. I would attribute this attitude in part to the (appropriate) self identification of many lighting people as artists, and it’s quite true that it’s not an easy thing to accomplish. But I hold that if we are successful in identifying a few basic measures of thermal comfort ( 5, not 1 ) , and that if we can devise a useful comfort rating system for them  (which we have done) we can do the same for lighting.

Measuring visual comfort will certainly be trickier than measuring thermal comfort, for at least two reasons. First, thermal comfort has a clear boundary condition- we’re either too hot or too cold and can’t function well if we’re very far out of the comfort zone. Visual comfort by contrast has a much wider range of acceptance, which is related to the second reason, our visual resilience. The second reason visual comfort is harder to measure is a cognitive one- our visual systems have evolved to be able to adjust visually and function reasonably well in a wide range of conditions, including the prevailing one in much of the built environment: poor quality, low contrast, poor color fluorescent overhead lighting. In most interior spaces bad lighting is still the rule rather than the exception, and many people don’t have a clear image of good lighting to reference by memory because there’s not much of it around.

The methodology for measuring visual comfort would necessarily rely on some individual “voting” mechanism, as thermal comfort currently does. This looks to be a user interface design issue for lighting controls. We have only begun to imagine the behavioral landscape in increased and more granular control of general lighting zones by occupants of open plan offices in commercial spaces. Will we be motivated to “vote” on whether we’re visually comfortable or not in our new smart lighting environment? Or will it seem like those annoying “rate your transaction” boxes that pop up online after every amazon purchase?

I believe that with the increase of cheap powerful sensors and new technologies like affective computing, we’ll be able to set our networks to learn what makes people comfortable with their lighting and HVAC by reading and analyzing what they do, and how their bodies (including faces and pupils) react unconsciously. In a highly flexible and configurable system, we should be able to extrapolate from behavioral data what people generally prefer and make appropriate level settings on actual behavior, rather than inaccurate assumptions about behavior.

I propose developing a standard similar to CBE’s Advanced Human Thermal Comfort Model- we could call it call it the Human Visual Comfort Model. 

Daylighting and Daylight Autonomy
Like Thermal Autonomy, Daylight Autonomy is the degree to which a building provides optimal lighting without electrical lighting systems. Fortunately this term has made its way into LEEDv4, where it's referred to as Spatial Daylight Autonomy, but according to a description of a session at Greenbuild 2014 posted on the USGBC website: “Currently; the design community is still unfamiliar with the process; requirements and implications for daylighting and energy design.” This sentence alone points out at least two problems- the fact that the design community in general is unfamiliar with the practice of daylighting, and the fact that from USGBC’s view, it’s primarily about energy, not comfort.

I am vocal about encouraging lighting designers to own “daylighting” as a building design practice. Indeed, many ( but by no means all )of the best ones do. But doing so means stepping outside your training and breaking out of your professional cage into the territory of the architect. This can be threatening and upsetting to architects and inspire defensive or dismissive behavior on their parts rather than the collaboration that should result in better design. They can’t be blamed really if their educational backgrounds did not include things like passive thermal or daylighting design, practical disciplines learned over millennia in building practice but forgotten in recent generations with the advent of glass facades and mechanical systems. It’s going to be difficult for many, but architects need to be lighting designers as much as lighting designers need to be architects- in fact there is quite a close relationship to the two professionally, as many lighting designers come to the profession through the practice of architecture. These often make the best lighting people because they understand, as all the best architects in history have, how buildings are inherently about light. There is still, of course ample room and need for specialization today in building. But the traditional practice of architecture, in most western culture at least, has been defined by the architect’s ability to hold a lot of general knowledge about what specialists do, and to manage them better precisely because of that specialized knowledge. It’s rather like an orchestral conductor knowing about bowing and fingering on the stringed instruments and breath control on woodwinds and horns despite having the piano as a primary instrument.

 Designing for daylight autonomy means following a well established practice for sustainable design- use available daylight, and control it well, which is of course a fundamental function of shelter. Unfortunately, “daylighting” today is a function for special consultants, rather than a fundamental one of architects, as it used to be before electric light was pervasive. I propose that if we must have specialists in daylighting, that they be lighting designers, as they understand how light affects people more than anyone else. In order for them to do this, they have to have a better understanding of architecture. Conversely, architects need to understand how to make buildings that deliver appropriate light as a primary function of design. Lighting designers are understandably too much focused on electric light, which is too often used too late in the design process to mitigate the less than optimal approach to daylight. And of course lighting designers and architects need to work together more closely in early design stages- this is simply not the common practice today.

Rather than only defining a building with appropriate daylight as highly energy efficient, which is about what it doesn’t do, we should define it by what it does do- how it provides a positive attribute everyone agrees is desirable in buildings- daylight. Using a daylight autonomy metric will not negatively affect energy efficiency, it will in fact end up increasing it. “Daylighting” as a specialized practice needs to go away and become again a standard part of what architects and lighting designers both do, and ideally do together, with visual comfort as a primary design goal.