Gathering and focusing light

A building’s skin acts as armour, as the moderator of light, and sometimes skin can also be structure. Can we consider merging these roles, detailing them with the strategies seen in nature? Brittlestars, such as Ophiocoma wendtii, have a covering of calcite crystals that function as effective armour as well as near optically perfect lenses (fig. 126). These focus light onto receptors below, so that the whole body works like a compound eye. Additionally, the brittlestars are able to control the amount of light coming in by means of chromatophores (pigment-filled cells) and adaptively tune the focusing of the lenses.¹⁶⁰ Could we create facades with an equivalent level of sophistication – controlling the amount of light entering the building and even redirecting the light to penetrate deeper into the occupied spaces?

It is often organisms that live in the lowest light conditions that demonstrate the most interesting adaptations, and provide inspiration for architecture. The rainforest plant Anthurium warocqueanum has evolved a covering of cells whose diameter, shapes and spatial layout create lenses over its leaf surfaces, which appear to be able to concentrate diffuse light onto a group of chloroplasts, aligned at the point of highest concentration. This strategy ameliorates the basic disadvantage of its growth habit: it receives no direct light because it lives near the forest floor, under the shadow of the dense canopy above.

Another solution is evident in giant clams. They have a dull-coloured shell and dazzling iridescent ‘lips’ that point upwards. The iridescence comes from cells called iridocytes, which reflect non-useful wavelengths of light and accurately distribute the useful light onto vertically arranged columns of microalgae.¹⁶¹ The algae exist symbiotically and photosynthesise to produce nutrition for the clam, representing a significant part of the mollusc’s energy budget. Looking for symbiotic lighting solutions, where crossovers between systems improve the overall performance, is a suggestive starting point.

Spookfish (Opisthoproctidae) split the problem of dealing with different types of light, with ‘diverticular’ eyes (fig. 127). These specialised, bizarre creatures seem unique: their heads resemble the transparent cockpit of a submarine designed by Tin Tin’s Professor Calculus and they are the only vertebrate known to use a mirror to focus images. Each eye is split into two connected parts: one part pointing upwards towards daylight and one part pointing downwards, with a mirror to focus the lower intensity light coming from bioluminescence.¹⁶²

Both Anthurium warocqueanum and the spookfish were sources of inspiration for Exploration and Julian Vincent when working on the Biomimetic Office. One of the aims was to make the building fully naturally lit – partly to reduce energy consumption but mainly for the well-being benefits offered to the occupants.

126. The brittlestar has evolved near optically perfect lenses over its skin, which function like a compound eye

127. The spookfish with diverticular eyes – who the heck designed that?

128. The Biomimetic Office by Exploration – inspired by a wide range of light-gathering examples in biology

The building was designed to ensure that every inhabitable part of the office floors was within 6 m of the nearest windows. This optimisation also included stair/lift/WC cores and a desire for full-width spaces, that are considered essential to allow larger clusters of people to work in creative groups. The glazing system optimised light transmission and minimised heat transfer by using transparent insulation above and below those parts of the window needed to provide views out. This led to a new form of glazing, using very thin curved panes that could deliver a 50 per cent material saving in glass. The most difficult challenge was how to get natural light into the lower floors. Anthurium led to the idea of lenses on the roof that could concentrate diffuse light into fibre optic tubes so that daylight could be conducted around the building to where it was needed – much like any other service. There are some products similar to this already on the market, but they all depend on the parallel rays of direct sunlight for their focusing. This is less appealing because, when there is direct sunlight, general illuminance levels are higher and getting light into the building is less of a problem – Anthurium offers the more interesting prospect of gathering light in diffuse conditions. The idea is now progressing as an independent research project. The spookfish led to the idea of incorporating a symmetrical pair of large-scale mirrors in the atrium to reflect light into the ground-floor and first-floor levels. The space under the mirrors presented an opportunity to create a dramatic auditorium that would add value to the building (fig. 128).

Minimising self-shading

129. Phyllotactic tower by Saleh Masoumi, based on the geometry of plants, which optimises access to light by minimising self-shading between leaves

A simple principle seen in plants, phyllotactic geometry (see Chapter 1), has been used to develop a building whose entire form is designed to harness light in a truly profound way. The repeating spiral, whose ratio is normally based on the Fibonacci sequence, has been used to great effect by architect Saleh Masoumi. He proposes phyllotactic towers, which meet the natural human desire for a private garden space for each home, and also maximise the possible solar gain, which could be harvested for energy (fig. 129). The phyllotactic arrangement means that, as in plants, each unit shades the other units from light and air to the minimum possible extent. Light, air and private outside space are crucial human requirements in high-density housing design and it could be that biology’s equivalent solutions could inspire very valuable innovations in this area.

Creating light and colour effects

Turning to how nature creates light and colour, the irrepressible glass sponge features again, in reliably spectacular form. Towards the base, the sponge has a large number of long fibres that anchor it to the sea bed. Many of these are fibre optic tubes (grown at ambient temperature and pressure) with optical quality comparable to, and much greater flexibility than, the relatively fragile human-made versions (manufactured with high temperatures).¹⁶³ Some of the tubes terminate in the sea bed with a prong structure comprising an array of lenses. The glass sponge has evolved a symbiotic relationship with a mating pair of bioluminescent shrimp that remain trapped within the structure for their whole life¹⁶⁴ and it is speculated that the glass fibres either transmit light from the shrimp out into their surroundings or light from bioluminescent bacteria in the sea bed up the structure of the sponge. Whichever version is correct, it is thought likely that the lighting scheme attracts food for the shrimp (they can’t exactly go foraging) and that the glass sponge benefits from the leftovers.¹⁶⁵ The glass sponge is a paragon for architects to aspire to in terms of structural, material and lighting sophistication.

Bioluminescence (the production of light by living organisms) is found in a large number of marine organisms, certain fungi, some bacteria and terrestrial animals such as fireflies. The last of these has already resulted in improvements to the design of light-emitting diodes (LEDs).¹⁶⁶ The clusterwink snail (Hinea brasiliana) produces bright flashes of light, which are amplified and diffused throughout its protective shell.¹⁶⁷ This could inspire the design of structural elements that also diffuse light, or simply more effective light fittings. There is intense speculation about the potential for synthetic biology to engineer bioluminescent organisms into elements of the built environment. This intriguing proposition may be challenged by the relatively very low levels of illuminance generated from bioluminescent organisms – spectacular in an otherwise pitch-black ocean but which would be virtually invisible in an averagely well-lit contemporary city.

Adaptive or stable structural colour

Cephalopods, such as squid and octopuses, extend their exceptional light manipulation attributes with shape-shifting camouflage.¹⁶⁸ Biologist Tamsin Woolley-Barker observes that ‘octopuses not only have a centralised light perception system (the extraordinary cephalopod eye), but they also have a decentralised system of light sensors distributed throughout the skin. The entire body of the squid is, in fact, a series of cameras, sensing light from every direction. The combination of powerful eyes and distributed light sensors allows the octopus to detect and match its background completely.’¹⁶⁹ Cephalopod skin contains a range of cells that manipulate ambient light passively, requiring much less energy than actively producing light. It is this characteristic that could lead to new forms of display screen that could cover the whole facade of a building and still use very little energy. Conceivably, buildings could dynamically blend into their surroundings as the colour of the light changes over the course of a day, and as the plants change over the course of a year.

Many striking colour effects in biology are examples of structural colour. Whereas most of the colour in synthetic surfaces is the result of reflection from pigmented material, structural colour is produced by the diffraction of different wavelengths of light from a nanosurface.¹⁷⁰ Nanosurfaces in nature show both structural hierarchy and 3D spatial arrangements at a scale smaller than an atom. While the practicalities of creating a biomimetic nanosurface are challenging, the prize is a much more dynamic colour effect with little or no energy and no pigments. To address the practicalities, self-assembly techniques have been successfully trialled¹⁷¹ by the biomimetic research group led by Professor Aizenberg to create nanostructures that resemble the architecture of the bright-green wing scales of the butterfly, Parides sesostris. They have also been inspired by the bastard hogberry’s fruit, with its dazzling colour effects. How this species got its name remains something of a mystery, since its Latinate name (Margaritaria nobilis) translates as ‘noble pearl’. What has been demystified is how to replicate its colour effects. Its iridescent blue is the result of a multiple layered cylindrical structure within each cell on the surface. This nanostructure produces light interference patterns, resulting in the reflection of vibrant (mainly) blue light. The scientists have managed to produce a fibre based on the maligned berry that changes colour when stretched, displaying all the colours of the rainbow.¹⁷²

Integrated approaches

The skins of biological organisms are directly analogous to the external walls of buildings: both perform multiple functions. The key challenge, I would argue, is to learn from the levels of integration and performance that can be seen in biological examples and combine that with the best that human ingenuity can deliver.

Two different integrated biomimetic approaches are currently being explored by a multi-disciplinary team involving the Harvard Graduate School of Design and the Wyss Institute for Biologically Inspired Engineering. The first proposal, put simply, is to combine all the required functional performance within a single glazed unit.¹⁷³ The Dynamic Daylight Control System (DDCS) combines millimetre-scale transparent light reflectors, that can be moved according to the sun’s angle, and the channels between them, through which fluid can be passed to reduce heat transfer (fig. 130). The light reflectors are made from flexible, transparent polydimethylsiloxane (PDMS), bonded to outer sheets of clear material so that, by moving the sheets relative to each other, all the reflectors move elastically – an elegant solution with minimal mechanical movement. Furthermore, the fluid can be controlled, such that it can be completely clear when desired or pigmented to reduce light transmission. The biological inspiration came from a profound understanding of how light is controlled in biology and from the way that blood vessels can transfer heat to, or away from, skin.¹⁷⁴ Prototypes have demonstrated impressive results: reduced glare, improved light penetration, reduced heat transfer and, by matching the refractive indexes, the reflectors are almost indistinguishable from the fluid.

The second solution, now in development, also by the Wyss/Harvard team,¹⁷⁵ pursues another strategy for adaptively tuning light and temperature simultaneously, and is also based on human vasculature and on the idea of adjustable optical properties seen in nature. But this solution utilises microfluidics for its operation. A clear microfluidic silicone skin, layered onto glass, can heat or cool the interior temperature according to how much fluid fills its microscopic channels. Astonishing ongoing developments show that this technology can be applied not only to window glass but also to solar photovoltaic panels. On windows, the thermal benefits do not affect the visual openness of the glass, something that is also important for solar panels, for operational rather than visual reasons: the sun needs to reach the panel, yet lowering the temperature makes the panel far more efficient at producing energy. From an architect’s perspective, it is important that the glass can appear perfectly clear, or its aesthetics can be altered by changing the properties of the fluid: particularly colour or reflectance.

A similar research project at a whole-building scale, led by Maria Paz Gutierrez at the University of California, Berkeley Department of Architecture, aims to integrate not just light control but also temperature and humidity control. The Self-Activated Building Envelope Regulation System (SABERS) project studies how to incorporate optical and hygrothermal sensor and actuator networks into a thin membrane. Gutierrez’s team have successfully experimented with ‘pores’ made from elastomeric material that can swell, providing more insulation, as temperature decreases. The intention is that the pores will also contain lenses that control light – reducing transmission as external light intensity increases and vice versa.

Conclusions

Light affects humans profoundly and, since so many people spend most of their time indoors, how buildings handle light has a direct influence on health and well-being. But the ability of the skin of a building to address not only the handling of light but the climate, the air and many other qualities is the central message in this chapter, as it is in Chapter 5 on thermoregulation. Ultimately, the skins of our buildings will need to integrate all these functions.

As well as considering the building’s skin, we have examined both the microscopic and the whole-building scales. Burgeoning research into the light-emitting and biosensing possibilities of bacteria encourage us to think of architecture in ecosystem terms, as do projects at the scale of buildings designed around light and around quality for inhabitants. The Biomimetic Office translated biomimicry ideas, such as the mirrored eyes of the spookfish, directly into architectural form. Other avenues, like the focusing lenses of Anthurium warocqueanum, hold promise for future research and development.

The active academic research communities whose projects have been explored here show enormous promise. In many cases, this foundational work extends to working prototypes, improving the chances and speeding up the process of turning these ideas into products that can be incorporated into buildings. As with all the biological examples we have studied, the evolved adaptations demonstrate what is possible and serve as an inspiring destination to aim for.

130. Dynamic Daylight Control System (DDCS) developed by the Harvard Graduate School of Design and the Wyss Institute for Biologically Inspired Engineering