Circa Diem

You can’t change the time of the day! The light you receive from the sun is exactly what your body needs. Connect at another moment to see this website evolve.


Human light

Light received at the eye regulates our neurophysiology through a non-visual pathway. A proper exposure to the natural day-night cycle - under which we evolved - is an essential part of healthy living and can have important consequences on sleep, mood, illness and productivity.

Circadian rhythms

Our body regulates itself through light exposure according to the day-night cycle. Hormonal and body temperature cycles all rely on the synchronization of our circadian rhythms.


Our retinal ganglion cells are most sensitive to the blue part of the visible spectrum, and respond differently depending on prior light history and patterns of light exposure.


To remain alert during the day, we need to be exposed to abundant white light, while we need dark nights for a steady production cycle of the melatonin hormone, essential to our health.

Health impacts

Light received at the eye affects our neurophysiological responses, with impacts on cognitive performance, alertness, mood and sleep, and on well-being and resistance to illness.

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Our daily exposure to light as well as its dynamics over time are a crucial element of our health and well-being. Light received at the eye fundamentally impacts our physiology, as our so-called biological clock – or more precisely the synchronization of our circadian rhythms – is heavily influenced by the information conveyed to our brain by dedicated photoreceptors present in the human eye. Only twenty years ago, a photopigment called melanopsin was discovered in the intrinsically photosensitive retinal ganglion cells (ipRGCs) of the human retina. These ipRGCs have the highest sensitivity to light in the blue part of the visible spectrum and, while being present in the retina, do not contribute to vision. Due to the distinct visual functions of rods and cones versus non-visual responses to light mediated by ipRGCs in the human retina, people with visual impairment may retain sensitivity to light for the synchronization of their circadian rhythms. Although ipRGCs mainly help us differentiate day from night, this function has major consequences on health and physiological well-being and improper light exposure can affect our circadian rhythms and have detrimental effects on our health and sleep.

Urban Light

Modern urban lifestyles disconnect us from the natural day-night cycle. Dense urban environments, especially when considering life underground, threaten our ability to enjoy a healthy and sustainable life by leading to an ever-increasing artificiality in our daily environment when it comes to light.

How cities shape light

Given our heavy reliance on electric rather than daylight, especially when considering life underground, the diurnal cycles we are experiencing tend to be socially-shifted rather than based on the natural day-night cycle.

Light and time in cities

The different phases of the day - morning, day, evening, night - have distinct effects when it comes to the impact of light exposure on our neurophysiology.

Indoor lifestyles

Unlike the natural day-night cycle under which we evolved, we are chronically light-deprived during the day by spending our time indoors, and exposed to excessive light in the evening and night.

Social jet-lag

Artificially bright evenings will have a tendency to prolong our biological day and thus to delay the onset of melatonin at night, a hormone essential to our sleep and to the resetting of our biological functions.

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No period in human history has seen a process of urbanization as fast and intense as the one experimented worldwide over the last few decades. Each year global cities receive millions of new inhabitants, most of them coming from both national and international migrations in search for job opportunities and the dream of a new life. From Shanghai to New York, Tokyo to Sao Paulo, this demographic stress results in areas of existing urban fabrics and their suburban landscapes being progressively substituted by new developments of high-rise buildings that literally darken the streetscapes and their associated interior spaces. Daylight is not only the most abundant and inherently renewable source of light, it is also considered necessary for any working or living environment to be acceptable for long periods of occupation. So while modern lifestyles have evolved towards electrically lit, densely built and indoor-dominated environments, there is fortunately an increasing awareness that health and wellness can be profoundly and durably affected by the quality of the built environment. This requires that human needs should be prioritized when designing or managing buildings and cities – which starts with these needs being better understood. We need bright mornings to synchronize our biological clock and adjust our sleep-wake cycle to the 24-hour clock. We need intense light during the day, so as to feel alert, to move and be productive, and keep our vigilance high. We need dim evenings to fight social jet-lag, an effect that is worsened by the increased use of electric lighting and screens that emit blue-rich light. We need dark nights for a high-quality sleep and a steady production of melatonin, that is highly sensitive to light exposure, so as to reset our biological functions and prepare ourselves for the next day.

Filtering light

Architecture and the urban fabric play a key role in the multi-dimensional relationship between us and the quintessential source of light – the sun and the diffraction of its rays in the sky. Not only do they control our access to light, they also re-shape this access in both space and time.

Harvesting daylight

The built environment filters available daylight by collecting and transporting it, then distributing it in interior spaces so that it can ultimately reach our eyes – thereby affecting our physiology.

Architecture as a filter

Architecture – and the craft and technology underlying it – has the ability to control our access to light by redirecting light rays through spatial form: in other words, it reshapes light for us.

Reshaping light

Taken to an extreme, reshaping light with filters can take multiple forms, from permeability through simple openings to advanced optical phenomenae like caustic patterns.

A continuum of daylight filters
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Refraction can create beautiful high-contrast patterns, such as those observed at the bottom of a swimming pool and whose shape is determined by the dynamic curvatures at the surface.

This principle of light-shaping through reflection and refraction of rays has been studied extensively for optical systems, such as cameras or microscopes that feature complex configurations of lenses and mirrors to re-direct light for imaging. When pushed to its limits, light shaping even allows transforming collimated beams emitted from the sun or an artificial light source into distinct and detailed images. Using advanced computational methods in combination with high-precision optical manufacturing, we can create free-form refractive lenses that precisely control each individual light ray to draw with light any desired image onto a curtained canvas. These light images get distorted again when moving either the light source or the lens, thereby creating mesmerizing visual experiences through a carefully orchestrated choreography of optical patterns.

This technology both embodies our ability to take control of our exposure to light and communicates about how important it is to care about it.

CIRCA DIEM experience

The CIRCA DIEM installation aims to contest the progressive disconnect of the contemporary city from the natural day-night cycle, rendering visible its implications for the human body through a unique choreography of high-contrast patterns, painted in light.

Light and time

By entering a cylindrical space that suggests being deep in an urban canyon, the visitor gets immersed into the passing of time through four phases of the 24-hour day – morning, midday, evening and night.

Painting with light

A sensorial experience, involving a dynamic choreography of light and dark, color, words and images, is generated by a novel light-shaping technology that precisely controls the patterns formed by light.

Experiencing light in cities

Complemented by sound, the visual experience alludes to the multiple dimensions of circadian rhythmicity for human citizens when it comes to their exposure to light.

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CIRCA DIEM raises awareness to the criticality of light-induced human well-being, which effectively applies to any dense metropolis in the world.

The visitor enters a cylindrical space through a curtained opening to be immersed in a dim environment. Looking up, a glimpse of the sky can be seen through a volumetric representation of a high-density skyline to convey the impression of standing underground or deep down in an urban canyon. Looking around, the visitor gets a sensorial experience of the passing of time through different phases of the 24-hour day.

Through a carefully choreographed movement of a light source to mimic the sun course inside the cylinder, light rays are refracted through seven specially-crafted acrylic freeform lenses, a light-shaping technology provided by Rayform SA, that form visible imagery and text on a curtain embedding a color-gradient. When an acrylic plate precisely faces its light source, the hidden information embedded in its surface structure becomes sharp and clear. But this is a furtive revelation, which gets distorted again and disappears by merging with the surrounding contrast lines.

These high-contrast patterns, painted in light, symbolize the effects that light can have on human neurophysiology in the different phases of the day: morning, midday, evening and night. These light effects are evoked differently in each of the four phases through a combination of color, light images and words, all alluding to the multiple dimensions of circadian rhythmicity in the built environment and to how they impact the humans inhabiting it. A discrete soundtrack adds to the experience by helping visitors get into a quiet, meditating mindset while experiencing the gentle rhythmicity of a day through sound.

The dynamic interplay between sound, color, light and dark creates an intensely visual and immersive experience. Further accentuated by the slow rotation of the freeform lenses, subtle and mesmerizing light dynamics are created, with dancing lines and areas of high visual contrast. The installation thereby exemplifies how light-shaping technology can be employed – to an extreme – to re-direct sunlight when designing deep spaces.


EPFL and HEAD-Genève have joined forces for this installation and include: Professors Marilyne Andersen and Mark Pauly, Heads of LIPID and GCM labs (EPFL), Professor Javier Fernández-Contreras, Head of Interior Architecture (HEAD-Genève), Alice Proux (Assistant at HEAD), Florin Isvoranu (Architect at GCM) and Megan Danell (PhD Candidate at LIPID).

Online experience & art direction
Aurélien Mabilat

Web development
Charles Chalas

Korean translation

Yunni Cho, Dong Hyun Kim

Photo Credit

Alain Herzog EPFL, HIDE Studio, Geraldine Quek LIPID/EPFL

Authors' bio

Professor Marilyne Andersen is the initiator of the project and heads the LIPID Laboratory at EPFL. Physicist by training, her research focuses on daylighting and its impact on people’s health, perception and comfort. She was formerly professor at MIT and Dean at EPFL.
Megan Danell
(M.Arch’20, University of Oregon) is PhD Candidate at LIPID, EPFL.

Professor Mark Pauly
heads the EPFL Geometric Computing Laboratory (GCM), where he initiated the research on light shaping mirrors and lenses. He is a co-founder of the EPFL spinoff Rayform SA that brings this innovation to market.
Florin Isvoranu
is an architect and designer at GCM.

Professor Javier Fernández Contreras
is an architect, critic and Dean of the Department of Interior Architecture at HEAD-Genève. His work explores the relationship between architecture, representation and media, with a specific focus on the role of interiors in the construction of contemporaneity.
Alice Proux
is Interior Architect, and assistant at HEAD-Genève.

Full Credits

This project was made possible thanks to the additional contributions from:


Leonid Slonimskiy (HEAD-Genève, Instructor); Damien Greder, Phi Nguyen, Camille Bagnoud (HEAD-Genève, Assistants); Elsa Audouin, Sarah Bentivegna, Robin Declerc, Azadeh Djavanrouh, Marina Ezerskaia, Thibault Krauer, Nourbonou Missidenti, Patrycja Pawlik, Louise Plassard, Patris Sallaku, Yichen Wand, Nobuyoshi Yokota, Léa Rime, Lubna Behey, Ségolène Davister, Débora De Almeida Borralho, Pauline Gueissaz, Gyeonghwan Hwang, Raphaëlle Marzolf, Vera Neuenschwander, Julie Reeb, Alain Van Garderen, Saëlle Venetz (HEAD-Genève BA/MA students)

Lens imagery

Romain Testuz, Yuliy Schwartzburg (Rayform SA); Romain Baumer (EPFL-ATME CNC mechanic); Geraldine Quek, Steffen Hartmeyer, Maha Shalaby (EPFL-LIPID PhD students); Clotilde Pierson, Caroline Karmann (EPFL-LIPID PostDoc researchers); Ankur Bordoloi (UniL PostDoc researcher)


Claude-Alain Jacot (EPFL-SLL Head of Technical Unit); Samuel Cotture, Stéphane Clerc (EPFL-SKIL Coaches); Pierre Loesch, Michel Teuscher (EPFL-PLTE workshop Heads); Stéphane Pilloud (Composite – and honey – expert); Filip Goč (EPFL-GCM Fabrication Manager); Tian Chen, Seiichi Suzuki, Davide Pellis (EPFL-GCM PostDoc researchers); Quentin Becker, Uday Kusupati, Yingying Ren, Ziqi Wang (EPFL-GCM PhD students); Gaspard Villa, Tom Schlatter, Damien Delespaul, Clément Vincent, Loic Delineau (EPFL BA/MA students); Alain Van Garderen, Débora De Almeida Borralho (HEAD-Genève BA/MA students); Camille Bagnoud (HEAD-Genève assistant); Alice Andersen, Lea Danko (High school students); Ugo Rombach, Chloé Desailly, Victor Tomaselli (University students); Yunni Cho, Steffen Hartmeyer (EPFL-LIPID PhD students); Dong Hyun Kim, Clotilde Pierson, Caroline Karmann (EPFL-LIPID PostDoc researchers); Vincent Belet (EPFL-LIPID intern); Laurent Chevalley (EPFL-ATME CNC mechanic); Pierre-André Despont, Yves Ruschetta (EPFL-ATMX workshop Head and mechanic)

Electronics, lighting and sound

Marie Limoujoux (sound artist); Laurent Deschamps, Théo Di Giacomo, Paul Becquelin, Alejandro Santa Cruz Paz, Sora De Sousa Pereira, Guillaume Dunant, Alexandre Stoll (EPFL-LESO IT and PLTE workshops Head and members); Marc Wettstein (EPFL-SKIL Coach)

Video production

Luis Levrato, David Miñarro (HIDE Studio); Yunni Cho (Korean translation, EPFL-LIPID PhD student)