The Neutral Image

    The neutral state is considered to be the closest possible approximation of a baseline of interaction between light and architecture. Within the example of the rectangular room, the baseline represents the range of effect that occurs when one face of the room is a single, perfectly smooth, uncoated, and uninterrupted pane of glass.

    Rather than describing a particular effect that occurs through the use of a mediating architectural device, the neutral image acknowledges the range of effect that occurs despite minimal architectural intervention. The notion of this inherent variability is evident in the writings of architects that address the role of light in their work. Natural light is presented as a body of information unto itself. In Thinking Architecture, Peter Zumthor recounts, "I want to think about the artificial light in my buildings, in our cities and in our landscapes, and I catch myself forever returning, like a lover, to the object of my admiration: the light that meets the earth from afar...".1 This light is the product of a history of interaction. After being scattered differently by the gasses and water droplets of clouds in our atmosphere, light arrives to the surface  of the earth and is transformed by our natural and built environments before it reaches the site of the architectural opening.

The range of operation that occurs within the immediate context of the project is augmented by seasonal changes and day to day atmospheric weathers. Similar shifts in our personal predispositions toward the perception of and attentiveness to effects of light affect the range of effect that we observe in the neutral state. Certain archetypes attract our attention more than others because of their rare forms of manifestation. The neutral state is often only the object of our attention in those moments when it threatens to disrupt our ability to attend to a task. 

    By acknowledging this inherent range of incident light that arrives to our architecture, one can acknowledge that the light of a single moment has certain properties, biases, and limits. It may change over the course of a minute, an hour, or a season, but natural light is never truly stagnant. Its interaction with designed devices is similarly transient. Some devices may perform consistently while others require specific circumstances in order to manifest an effect that exists beyond the neutral range. 

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1.  Peter Zumthor, Thinking Architecture, 3rd ed. (Basel: Birkhauser, 2010), 89.

The Simple Image

    The simplest of all images formed in geometrical optics is the shadow, which occurs “when an opaque object in the path of a light source prevents the light source from traveling through to the surface behind the object.”1 This description may seem simplistic, but it establishes the key relationships that exist between architecture, light, and object. It is quite common to see studies done in environmental plugins such as Ladybug for Grasshopper that depict light in terms of absolute light and absolute shadow (umbra). Though architects are commonly interested in the white, daylit portions of these studies, this archetype encourages architects to instead consider the movement of the shadow image over the course of time and to expand its rigid, black outlines to include the consideration of the softer, layered penumbras that are an integral part of our observation of objects in space.

The role of architecture in forming the shadow primarily lies in framing natural light as it enters a space and interacts with the objects within it. It acts as a filter through which the single, distant, and highly directional light of the sun can be instantaneously operated upon and controls the number, size, and proportion of the sources of natural light that illuminate the interior. Though the directionality of the light is dependent upon the time of year and amount of light scattering (2) that has already occurred due to weather, the points from which light enters a room can have a significant impact upon the appearance of the shadow image.

In a way, the shadow inscribes the presence of the architecture on its own interior skin, and never fails to record the passage of time until artificial light sources control the image instead.

All obstacles, furniture, louver, or screen, are subject to produce shadows of variable size and definition. Architecture determines, to a certain degree, what the nature of the produced image will be. For example, based on the sources of light produced by the architecture, the image can be fragmented, smoothly gradated, or nonexistent. These conditions can be altered by increasing the number of small sources, changing the proportion of the light source, or changing the distance between the source, object, and nearest surface. In the event that a screen is placed directly in front of the source, the image of that entity will appear to be projected onto the objects of the room – depending on the directionality of the source, its image may be preserved or, on a diffuse day, it may only affect those surfaces that it is closest to. The shadow is useful in exposing to us the agency of architecture in framing the light of the sun.

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1.  Galen Duree Jr., Optics for Dummies (Indianapolis: Wiley, 2011), 60. Galen Duree is a professor of physics and Optical Engineering Director at the Centre for Applied Optics Studies Rose-Hulman Institute of Technology.

2. Ibid., 48.

Caustic Light

Caustics are formed by light rays that are reflected or refracted by a curved surface or lens. The phenomenon, often visible when light passes through a glass or at the bottom of a pool, exists because of the interaction of uniformly directional light with the fluidly curved surface. In David K. Lynch and William Livingston's book Color and Light in Nature, the surface of water is described as a series of positive and negative lenses. The positive, convex lenses act to concentrated light while the negative, concave lenses direct light away from the interstitial areas, producing a vibrant network of concentrated curves of light.1

Architecture typically plays a passive role with respect to this archetype of light effect. Incidences of caustic effects are often happenstance, and can be dismissed or heralded as serendipitous coincidence. However, it is difficult to deny the curiosity and wonder that is evoked in the viewer when concentrations of light appear in the umbra of the shadow image despite our contradictory common understanding of shadows as being indicative of an absence of or an obstruction of light. The caustic therefore appears as a true secondary layer of information.

Unless viewed in extremely bright ambient conditions, the caustic will always appear to the viewer as superseding the brightness of proximate light effects.

The etymology of the word caustic lies in the Greek words kaiein, 'to burn', and kaustos, 'combustible'. Though caustics require some computational power to replicate, it is possible to digitally reproduce and manipulate their most common forms. This changes the role of architecture from passive recipient to possible instrument with which to tune these fine structures of light.

Though forms can be generated that produce intricate patterns and lines of light, caustic propagation can be resolved in great detail. Research conducted by the Computer Graphics and Geometry Laboratory at the École Polytechnique Fédérale de Lausanne shows that any desired photographic digital image can be reproduced in caustic form when a transparent or highly reflective material is milled with the geometry that computationally corresponds with the image's light and dark areas. Upon exposure to a direct light source, the image is revealed.2 This research, though as of yet tentative in its proposed application, marks the first foray of architecture into the realm of active engagement with caustic phenomena.

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1.  David K. Lynch and William Livingston, Color and Light in Nature (Cambridge: Cambridge University Press, 2004) 93-94.

2. Thomas Kiser et al., "Architectural Caustics - Controlling Light with Geometry," EPFL Computer Graphics and Geometry Laboratory, accessed April 4, 2017,
http://lgg.epfl.ch/publications/2012/caustics/ArchitecturalCaustics_AAG.pdf.

The Specular Image

The specular image is formed when light information is redirected from its incidental direction to the occupant. There is an intrinsic relationship between the image and surface that holds the optically virtual image. The fragility of the image is matched only by the necessary order of the smoothness of the receiving surface. In order to offer the image to the viewer as if it were its own, the surface must be optically smooth, and is so only "if any surface feature height... is much smaller than the wavelength of the incident light."1 The preservation of the image is possible only because the directionality of all incident rays relative to one another is preserved.

Architecture must very carefully consider the incidental outcomes of introducing mirror surfaces in space. In "The Poetics of Light," Henry Plummer cautions against mirrors: "The plane mirror is always susceptible to squandering its incident light and, by complete reflection, annihilating its very existence."2 Not only does the image have the power to supersede the surface, but the precise directionality of the reflected rays will often render the intended image only perceptible to the viewer from a certain position.

In a sense, the mirror will fulfill its intended role only through the specific, successful choreography of the orientation of both the architecture and the body. The mirror also has the ability to fragment and distort. When two different choreographies of surface orientation are placed next to one another, the virtual image disrupts the real image. Plummer addresses this strange phenomenon in his analysis of the mirror 'windows' of Amalienburg: "...each slippery sheet is actually a terrain of cold silver, shimmering and shadowy, possessing radiant images that are somewhat warped, broken up, and disarranged".3 His evocation of the mirror as a terrain of cold silver is not without value - the life of the mirror outside its designed viewing is integral to the atmosphere of the space.

The limitation of the specular image lies in its flattening of information and fleeting existence. The precision of the archetype is wholly determined by the quality of its host surface. As the optical smoothness of the surface deteriorates, so does the quality of the image, until the image is indiscernible and another archetype is born.

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1.  Duree, Optics, 46.

2. Henry Plummer, “Poetics of Light,” A+U December Extra Edition (December 1987): 25.

3. Plummer, "Poetics of Light," 25.

The Secondary Source

When the surface feature height of the surface is larger than the wavelength of incident light, the incident rays are reflected at various angles because they no longer share the same surface normal.1 Any image carried by the incident light rays is destroyed as it interacts with the heterogeneously textured surface and is fragmented into many directions. The use of a surface as a secondary source of light is part and parcel of Hervé Descottes' "Six Visual Principles of Light".2 He aptly describes the power of this archetype through an example: "Consider the moon: it does not emit light on its own, but the sun's light reflected off the moon's surface creates what we recognize as moonlight."3 In Architectural Lighting Design, Descottes establishes that the process by which an object returns the light that it has received from a source of light to the eye of the viewer is quantitatively measured as luminance.4 He claims a sense of hierarchy can be developed within a space when surfaces of varying luminance levels are placed in proximity with one another.5

Architecture mediates the production of this archetype at two places.

The source of light must be framed and placed into a dialogue with a receiving surface before that surface can act as a seconday source of light. The architecture can express or conceal this relationship and can choose to display the secondary surface as a diffuser or conceal it and instead present it as a site of registration. The relative intensity of the light that is directed to the eye of the viewer can produce effects of both sharp and subtle layering of both surface and object.

It is interesting to note that the secondary surface can be used to itself perpetuate the production of silhouettes, one form of the simple image, within a space. A concealed source that washes a wall with light can reduce the appearance of a three-dimensional object to a crisp, dark outline of its potentially rich form. The secondary surface can thus be revealed as one of the most active and illusory of the seven archetypes. The range of luminance is so great as to include that amount of light information which imposes a kind of violence on our senses as well as a total absence of light information which reduces an object to an edge.

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1.  Duree, Optics, 48.

2. Hervé Descottes and Cecilia E. Ramos, Architectural Lighting: Designing with Light and Space (New York: Princeton Architectural Press, 2011).

3. Descottes, Architectural Lighting Design, 31.

4. Ibid., 30.

5. Ibid., 34.

Textural Light

The transition from the archetypical effect of the uniformly luminous secondary surface to the more variegated textural light is once again due to an increase in the order of surface feature height of the receiving surface. When the surface features, surface geometry, or surface quality or patina are such that parts of the surface will collect or hold light while other areas are recessed or lost in shadow, textural light is at play. Even minute details can be revealed by a source that pushes light across an architectural surface.

Architecture can inform the intensity and directionality of incident light in order to express the materials and methods of its construction. Textural light most commonly exists when a source is narrowly framed and deployed along the edge of the surface plane with few or limited sources of light illuminating other areas of the room. Few additional sources are needed as this archetype of light often acts as a fractured secondary source, providing sufficient illumination for those tasks that do not require precise illumination. In The Eyes of the Skin, Juhani Pallasmaa describes materials that lend themselves to textural effects of light: "Natural materials - stone, brick and wood - allow our vision to penetrate their surfaces and enable us to become convinced of the veracity of matter."1

In some ways, the depth that is apparent when light interacts with these materials is the opposite of "the architectural mirror, that returns our gaze and doubles the world, [and] is an enigmatic and frightening device."2 Details in construction that capture the human endeavour of building are equally important in the realization of this archeytpe. In Peter Zumthor's renowned Therme Vals project, on-site masons were first disappointed when the slit-like apertures that bathe adjacent interior stone surfaces in light were opened. "The shafts of light washed the walls of their finished work causing tiny irregularities in the stone bond to cast dramatic shadows. But watching optical illusion, which at first seemed to suggest a job poorly done, soon turned into pure delight."3 The power of this archetype often lies in the subconscious history that is imparted to the viewer as they observe the phenomenon, be it a history of labour or fabrication.

Textural light is a friend of the shadow - it is through a balance of light and shadow that it exists, and it can continue to exist when this relationship skewed toward shadow until just the barest hint of direct or filtered light is registered by the non-uniform surface. Textural light engages both our visual and visceral senses of experience.

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1.  Juhani Pallasmaa, The Eyes of the Skin: Architecture and the Senses (Chichester: Wiley-Academy, 2005), 31.

2. Ibid.

3. Sigrid Hauser and Peter Zumthor, Peter Zumthor Therme Vals (Zurich: Scheidegger & Spiess, 2007), 113.

Dispersed Light

The archetype of dispersed light occurs when the wavelengths or colours of light that combine to produce sunlight are visibly separated, isolated, or selected. These effects can occur due to a variety of optic phenomena, but can most commonly be observed by way of dispersion, when the effects of minor variances among the indices of refraction for shorter wavelengths (such as blue light) and longer wavelengths of light (such as red light) are exacerbated. Because the indices of refraction increase or decrease alongside an increase or decrease in the wavelength of incident light, the paths of various wavelengths are bent to a greater or lesser degree as they pass through different media (per Snell's law).1 This effect is significant in the engineering of optical instruments whose operation depends upon refraction, (2) but is often only visible in architectural settings when the geometry of the medium (generally glass) that light passes through exaggerates the effect. When one uses a triangular prism to disperse light, the effect is observable because different wavelengths of light will continue to travel in different directions upon exiting the prism. In the case of a prism with parallel sides, the various wavelengths of light will be inversely dispersed at the second surface and will therefore continue on in the same direction with little evidence of any separation of wavelengths.

Architecture can facilitate the production of this archetype through the geometry of glass and glass-like materials. The effect commonly occurs when the edges of glass architectural artifacts are beveled, creating prisms. If the prism is stretched, the effect will diminish as the two planes become increasingly parallel. The archetype therefore has the greatest potential for impact through small or arrayed instances. This limitation can be circumvented through the use of dichroic filters. These materials are typically polymers that absorb much more light in one linear polarised state than the other perpendicularly oriented state. As Duree describes, this "process of selective absorption is very much dependent on the wavelength of the light."3 James Carpenter uses dichroic films in his 1995 facade project, Dichroic Light Field. The dichroic film on each of the two hundred and sixteen fins that project from the mirror-like screen transmits one half of the visible light spectrum while the other half is reflected.4 This polarisation of light provides the means by which to achieve a variation of the archetype, and deploys it in combination with the specular image archetype to register ambient lighting conditions while simultaneously operating on incident light.

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1.  Duree, Optics, 50.

2. Ibid., 54.

3. Ibid., 109.

4. Sandro Marpillero, James Carpenter Environmental Refractions (Basel: Birkhäuser, 2006), 41.