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“Light is the opium of the architect and shadow its form.” (Ian Ritchie, 2002)
“Shadows are holes in light.” (Ian Ritchie, 2002)
“Like an object, moving through water, light cuts through shadows only to leave shadows in its wake. Light and shadow belong together.” (Ian Ritchie, 2001)

Light comes continuously from the sun, directly or reflected by the moon; from lightning – the flash of light that accompanies an electric discharge in the atmosphere, or is man-made. There are some species that emit light through fluorescence and bioluminescence (firefly).

Light as we use it in architecture is perceived, not directly, but through reflecting surfaces.

Homo sapiens sapiens acts as homo faber, and one of our ancestors’ early works was to make light in the form of fire. Human vision, honed over millions of years without artificial light, was now subject to extended periods of use, and this fire-light made homo faber the most dominant species on earth – to the point where homo faber now threatens the survival not only of his species, but also other life on our planet.

Light chases away darkness, but creates shadows in the process, and these shadows in turn frame the pools of light. Darkness is never far away.

The history of architecture can be described as the story of the way day and sunlight enters into buildings and reveals through shadow the spatial composition and forms within. Sunlight allows space and form of architecture to change. Through light and shadow architecture acquires shape and meaning. Light reveals a building’s contours and shadow, its depth.

Light is the material of architecture through which we can best appreciate the nature of space, surface, colours and objects. Perhaps textures are felt as much through the skin as through the eyes.

When we left the cave, we constructed our own walls and a roof. We saw for the first time our walls from the outside as well as the inside. We made openings in them and the roof to let the daylight in. Later we put glass in these openings to keep out the rain. Throughout all this time we decorated our solid walls with signs of our changing culture, and used sunlight to illuminate through the glass walls.
We lived by the diurnal and seasonal rhythms of temperature and light. We moved from fire to oil lamps over a very long period, and then, in the 19th century the electric lamp arrived, and through Mr Edison, a system to light the world.
In the same century we were technically able to dismantle the walls upon which we inscribed our culture and make them and the roof entirely of glass, held up by thin strips of metal.
Since the industrialisation of lamp manufacture there has been an exponential growth in the amount of artificial light sources on the earth resulting in a continuing decline in the zones of shadow and darkness. In architecture, the dramatic increase in the use of glass and other translucent materials to wrap buildings questions the very significance of shadows.

There has been a great deal of technical and aesthetic refinement of glass architecture since the 19th century, and during the 20th century architects have had more and more freedom to design how much opacity and transparency they want in buildings.
The architecture that emerges from this freedom seems rarely influenced by artificial lighting – but it should be. The scope to exploit the multitude of surface treatments that glass can carry, together with the innumerable developments in intelligent and information systems which can, and will increasingly, be integrated with walls offers enormous scope for artificial lighting. Many of our own projects have proposed such integration, and these experiences, and our appreciation of light artists working at the threshold of human sight, such as James Turrell, have led us to think more about artificial lighting environments than hitherto. It is vital that architects imagine the spaces they are creating with knowledge and feeling of how the sun will transform them during the day, and how artificial light needs to be designed either to support this, or to create a completely different environment.

I believe that lighting designers should always work with nature’s own light pen – the sun – as the basis for any lighting composition. This may sound paradoxical.
It is not through defining the lumen output required upon a surface that the lighting designer begins – that is for those who formulate regulations.

Natural light is dynamic, to be tamed and framed, manipulated or left free by both architect and lighting designer. This means, quite simply, that architects should now be able to work with lighting designers on the same conceptual wavelength.
Design collaboration with sensitive, skilled and professional colleagues is both a pleasure and a necessity. Good lighting designers are essential to the architectural design team.

Our empathy lies with the lighting designer who says that the longer we keep the lights switched off the better we feel. And of course less energy will be consumed. If we allow the natural environment to be the instrument of design at all scales, then our designs will be more intelligent and more responsive to our senses.
The challenge to lighting designers has never been greater – to help create wonderful spaces both inside and outside our walls wherein we can frame our dreams and display our culture.

Our perception of spaces and surfaces differs greatly between sunlight and moonlight, artificial light and fire or candlelight. The sky during the phase transitions between day and night provides us with some of nature’s most magical moments. On a different scale, so too does the flickering candle flame, or watching the slow death of a fire.
The enduring candle is testimony to our reluctance to relinquish the fire-light, the contact with nature and the romantic atmosphere that it helps create – love and hope live in that flickering light and perfume. Light is hope and darkness fear, yet all the darkness in the world cannot extinguish a single candle.

© Ian Ritchie, July 2000 (foreword to Lightbook, Brandi & Geissmar-Brandi, Birkhauser, 2001)


Man is an ‘optic’ animal. It is generally agreed that about 85% of human impressions are visual. It follows that being able see well is essential to allow us to perform at our best.
The human eye is a remarkable bio-machine, though there are others in the animal kingdom which can have far greater specific powers, such as acuity. It is capable of adjusting to a wide range of light levels – from sunlight (100,000lux) to candlelight (10 lux) to moonlight (0.1 lux).
However, for most human tasks, between 50 and 1000 lux suffices; only exceptionally focused work will require more.

The human visual system responds to the light in the electromagnetic spectrum with wavelengths ranging from 380 to 770 nanometers (nm). We see light of different wavelengths as a continuum of colours ranging through the visible spectrum: 650 nm is red, 540 nm is green, 450 nm is blue, and so on. The human eye can detect light between 200 nm to 900 nm, but most of the sunlight that reach the earth’s surface lies between 400 nm and 700 nm because the atmosphere absorbs both longer and shorter wavelengths.

“The sensitivity of the human eye to light varies with wavelength. A light source with an irradiance of one Watt/m2 of green light, for example, appears much brighter than the same source with an irradiance of one Watt/m2 of red or blue light. In photometry, we do not measure Watts of radiant energy. Rather, we attempt to measure the subjective impression produced by stimulating the human eye-brain visual system with radiant energy.

This task is complicated immensely by the eye’s nonlinear response to light. It varies not only with wavelength but also with the amount of radiant flux, whether the light is constant or flickering, the spatial complexity of the scene being perceived, the adaptation of the iris and retina, the psychological and physiological state of the observer, and a host of other variables.

Nevertheless, the subjective impression of seeing can be quantified for “normal” viewing conditions. In 1924, the Commission Internationale d’Eclairage (International Commission on Illumination, or CIE) asked over one hundred observers to visually match the “brightness” of monochromatic light sources with different wavelengths under controlled conditions. Taking an average of the measurements results in the so called Photopic response of the perceived ‘average’ human observer is shown in graph below.

The curve on the left shows the response to low levels of light. The shift in sensitivity occurs because two types of photoreceptors, cones and rods, are responsible for the eye’s response to light. The curve on the right shows the eye’s response under normal lighting conditions and this is called the Photopic response. The cones respond to light under these conditions and they are also responsible for human colour perception.

The curve on the left shows the eyes response to low levels of light and is called the Scotopic response. At low level of light, the rods are most active and the human eye is more sensitive to any amount of light that is present, but is less sensitive to the range of colour. Rods are highly sensitive to light but are comprised of a single photo pigment, which accounts for the loss in ability to discriminate colour.” (source: Andor Technology)

Lighting Design Criteria

Lighting design and its management is to provide the optimum quantity and quality of light to help create the architecture, but also to provide it to users at the lowest operating cost.
Understanding and predicting how a lighting system will operate is fundamental to good design. The quantity of light (light output and light levels), the quality of light (brightness and colour), and fixture efficiency (electrical efficiency and how much light leaves the fixture) has to be well understood if a complete lighting picture is to be described.

Quantity of Light

Luminous Flux (Light Output). This is the quantity of light that leaves the lamp, measured in lumens (lm). A number of factors affect a lamp’s light output over time – lamp lumen depreciation, lamp-ballast interaction, variable supply voltage, dirt or dust, and the ambient temperature in the fixture. Lumen output is a term also used to describe a fixture’s light output, not just that of a lamp.
Illuminance (Light Level). This is the amount of light measured at the work surface. It is measured in lux (1 lux is 1 lumen /sq. m). It is a function of the lamp output, the room’s surfaces and their reflectance, and room size/proportion.

Quality of Light

Luminance (Photometric Brightness). The light that we actually see, brightness can be measured as the light leaving a lamp, or the light reflecting from an object’s surface. If not controlled, brightness can produce levels of glare that either impair or prevent a desired task being performed. Glare can be described as direct or reflected glare, which can then result in discomfort.. Direct glare comes straight from the light source. Reflected glare shows up on the task itself, such as a computer screen. Disability glare prevents vision.
Colour. The colour quality of a lamp is expressed as its Colour Temperature rating and Colour Rendering Index.

Fixture Efficiency

There are two main considerations in assessing a light fixture’s (luminaire’s) efficiency:

  1. electrical power (W) transformed into light (lumens) and is often expressed in lumens per watt (LPW or lm/W); and,
  2. light transmission to the work surface.

When lighting designers apply the results of efficiency to actual system operation (e.g. to determine the operating costs of an installation (or cost savings of a retrofit), knowing the energy consumption is now crucial. Energy use of a lighting system is the product of input wattage (W) x time (hours of operation during a year).


Input Wattage 100W
Lumen Output 10,000 lm
Efficacy 100 LPW (10,000 lm ÷ 100W)
Hours of Operation 3,120 h (Say: 5 days/week x 12 hours/day x 52 weeks/year)
Energy Use 312kWh (100W x 3,120 hrs/year)
Utility Charge/kWh £0.06 (UK tarrif c.2004)
Energy Cost/Year £18.72 (312kWh x £0.06/kWh)

The luminaire’s physical design characteristics will affect how much light leaves the fixture and how much arrives at the work surface. Factors that need to be considered include: shape, material reflectance, number of lamps inside the luminaire (and how close they are to each other), and whether glare shielding such as a lens or louvre is used.

To compare fixture efficiencies in a given environment, designers often use the coefficient of utilization (CU). This value shows the percentage of lumens produced by the lamps that reach the work surface after light is lost due to the fixture’s efficiency.

© Ian Ritchie 2004