The idea to write this blog came to me after I read a recent fascinating article in Terrapin Bright Green about the concept of alliesthesia and why it matters for building design.
The article in question focuses primarily on the thermal aspect, defining alliesthesia as “the influence that dynamic thermal environments can have on creating enhanced levels of occupant satisfaction, compared to static and uniform environments, especially moving beyond “neutrality” to create thermal pleasure.” In more comprehensible terms, temperature variations that take us from a slightly uncomfortable thermal state to a comfortable one are perceived as pleasant. Inversely, uniform and constant thermal conditions throughout the day and year might not satisfy our needs.
An easy way to understand this phenomenon is to imagine yourself outside, sitting on a bench in the sunshine, on a nice summer day. The sun is warming your skin slightly, maybe a little bit too much. And suddenly, you feel a light breeze on your face. The feeling is pleasant, right? However, we wouldn’t be as likely to enjoy such a nice moment if that same breeze was blowing on us constantly.
This phenomenon is also observed in relation to other physiological sensations like hunger or thirst. For example, a glass of water is extremely pleasant to a dehydrated person, but for someone who is no longer thirsty, the pleasure derived from that glass of water is greatly reduced.1
A theory applicable to other comforts?
One of the questions that occurred to me very quickly after reading the article was: what about other stimuli, like light? Does the alliesthesia phenomenon apply to them too? Do human beings also need variability in lighting and visual conditions to feel content?
Look at the photo below:
Does this type of space look welcoming and comfortable to you? Can you really see yourself spending all your workdays there? Personally, no highly touted scientific study is needed to convince me that I wouldn’t be very happy in this type of space. Intuitively, therefore, we could say that the answer to the question of needing lighting variability is yes.
After some searching, I’ve found that publications on this subject are surprisingly scant. That said, the publications in question seem to confirm the existence of a type of visual “alliesthesia.” Although its physical and physiological mechanisms differ from those of alliesthesia in a medical sense and from thermal alliesthesia, it still appears that lighting variations in a space are more appreciated and beneficial than uniform and static lighting conditions.
From a physiological standpoint, we now know that dynamic lighting like sunlight is beneficial for the non-visual effects it generates (if you’re lost, feel free to read this article). And from a psychological and emotional standpoint, lighting variations over time and space strongly influence our perceptual experience of a space. Studies have shown that a certain diversity in lighting conditions (intensity, distribution) has a positive impact on our impressions of the quality and interest of a place.2 Other publications3 refer to several studies showing that we appreciate moderate levels of sensory variability in our environment, including light, sound, and temperature variations, while environments with no sensory stimulation or variability can be sources of boredom and passivity.
Natural light generates a unique visual and sensory experience in the central courtyard of the Queen Elizabeth II British Museum (Source: https://blog.britishmuseaum.org)
What is the impact on building design?
The introduction of the alliesthesia phenomenon in 1971 by Cabanac4 contributed to a reexamination of how our interior environments and their thermal conditions are designed. The longtime rule was to control the interior temperature of buildings artificially so as to maintain it around a single preset, theoretically optimal temperature. Alliesthesia now opposes this static approach to thermal comfort, as does the adaptive approach to comfort, according to which people can adapt to a certain amount of discomfort, by adjusting their clothing or changing locations, for example.5 These opposing approaches have (re)-paved the way to designing buildings that are not climate-controlled but rather ventilated naturally. Furthermore, if buildings have access to sunlight, this results in possible thermally variable conditions, similar to those found outdoors and therefore more appreciated by the occupants.
When it comes to visual conditions with variations in lighting, one immediately thinks about daylight! Intrinsically dynamic in intensity, color, and direction, it is the most obvious answer to designing indoor environments that offer temporal and spatial variability of lighting conditions. Large windows and shallow spaces can take the greatest advantage of natural light. Bear in mind, of course, that this light has to be intelligently controlled so as not to generate extreme differences that would cause distraction and discomfort. Finally, when daylight is not enough, “biodynamic” lights, whose color and intensity are variable through the day, can be considered.
Dynamic variations in daylight from sunrise to sunset (Source : https://community.smartthings.com/t/circadian-daylight-smartthings-smart...)
Following these rules of good practice can make it possible to limit spaces with uniform lighting environments involving predominantly electric lights. This situation is observed primarily in many office spaces, where the lighting is on from morning to night and controlled so that it adheres to preset light levels, based exclusively on visual performance criteria (for example, 300 lux in offices, considered by standards to be the minimum needed to perform a visual task correctly and without eye fatigue). Doubtless this last point should be reexamined, as was previously the case for the thermal design of spaces.
Positive effects demonstrated on occupants
A number of studies have shown the positive impact of indoor spaces with variable ambient conditions on the comfort, wellbeing, and even cognitive performance of people. Furthermore, it is interesting to note that thermal variability and dynamic light are part of the main principles of biophilic design,6 which is intended to improve the health and wellbeing of a building’s occupants. For more details, I urge you to read the preceding blog on this subject, if you haven’t already done so!
In conclusion, and to illustrate the difference between an environment with “neutral” but perfectly constant conditions and an environment with variable ambiances offering multiple sensory stimuli, here is a metaphor from L. Heshong7 that speaks strongly to me, since I’m an avid foodie and a lover of gourmet cuisine:
“A parallel might be drawn to the provision of our nutrition needs. Food is as basic to our survival as is our thermal environment… It is … theoretically possible to provide all of our nutritional needs with a few pills and injections. However … no one would overlook the fact that it also plays a profound role in the cultural life of people. A few tubes of an astronaut’s nutritious goop are no substitute for a gourmet meal… They are disconnected from all the customs that have developed around eating… The thermal environment also has the potential for such sensuality, cultural roles, and symbolism that need not, indeed should not be designed out of existence in the name of a thermally neutral world”
Eloïse Sok is Concept Creator in the SageGlass Europe & Middle-East Team. She holds a Double-Degree in the Engineering field from Ecole Centrale (France) and Tsinghua University (China). Her main interests include sustainable architecture, daylighting and occupant’s comfort. Her motto: “Passion is our best strength!”.
1 from Dear R (2011) Revisiting an old hypothesis of human thermal perception: alliesthesia. Build Res Inf 39(2):108–117
2 Rockcastle, S. et al. A Simulation-based workflow to assess human-centric daylight performance, SimAUD 2017 May 22-24 Toronto, Canada
3 Heerwagen, J.H. Investing In People: The Social Benefits of Sustainable Design. Rethinking Sustainable Construction. Sarasota, FL. September 19-22, 2006
4 Cabanac, M. Physiological role of pleasure, Science 17 Sep 1971: Vol. 173, Issue 4002, pp. 1103-1107
5 From Dear, R. Thermal counterpoint in the phenomenology of architecture – A Phsychophysiological explanation of Heschong’s ‘Thermal Delight’, 2014
6 14 Modèles de conception biophilique [14 biophilic design models], Terrapin Bright Green, 2016
7 Heshong, L. Thermal Delight in Architecture, 1978