n the beginning, as the Earth formed 4.5 billion years ago from the condensation of a cloud of primordial cosmic dust and gas, its surface was initially bitterly cold and dark. As the dust slowly settled and swirling gases began to form a primitive atmosphere, the first glimmer of light broke through the gloom to illuminate a landscape torn by earthquakes and volcanoes and ravaged by fierce electrical storms. And then there was light, as the Bible says. Since then, the Earth has been illuminated by light from the Sun by day, when it reaches the Earth’s surface directly, and by night when it arrives courtesy of reflection from the surface of the Moon. According to scientists, we can expect to continue to enjoy the Sun’s generous bounty for several billions of years to come, or until we render the planet uninhabitable – whichever comes sooner!

Light

Visible light is only a small part of the electromagnetic radiation which originates from the Sun, from our own galaxy and from more distant galaxies, subjecting the Earth to continuous bombardment. The electromagnetic spectrum extends from gamma and X-rays through ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves.

The Earth is constantiybombarded by electromagnetic radiation, but much of thisradiation – including some visible light – is filtered out by the atmosphere before itreaches the Earth’s surface

While the Sun appears yellow to us on Earth, a simple rainbow demonstrates, by refracting sunshine through rain water droplets, that the light emitted consists of a continuous spectrum of colours ranging from violet to red. Closer scientific investigation, using a prism instead of water droplets and a spectrophotometer instead of the human eye, shows that the spectrum actually extends continuously beyond the visible colours into the ultraviolet at one extreme and blends into the infrared at the other extreme. Such measurements show that the colours to which our eyes are sensitive have wavelengths in the range of about 300 nm to 750 nm (1 nanometre, or nm, equals one billionth of a metre). Like other forms of electromagnetic radiation, visible light The visible spectrum can be characterised in terms of its wavelength and amplitude. The wavelength determines its hue -what the human eye perceives as its colour, e.g. as opposed to, while the amplitude denotes the brightness of the colour.

As its spectral distribution curve shows, the reason that the Sun appears yellow is that the intensity of light radiated by its surface gases is a maximum at wavelengths near 500 nm, in the yellow part of the spectrum. The Earth’s atmosphere – the gaseous envelope which surrounds the solid body of the planet – acts as a filter to the Sun’s radiation, the ozone layer fortunately absorbing much of the harmful ultraviolet radiation, while water vapour absorbs some radiation in the infrared region and at several parts of the visible region. High levels of atmospheric pollution in the vicinity of industrial areas can also reduce the quality of light reaching the Earth’s surface.

Light passing through a uniform medium, like space or the Earth’s atmosphere, travels in straight lines. This is not the case, however, when it passes, at an angle, from one medium to another with a different refractive index, as in the air to prism example mentioned already or in the common case of light passing from water to air – an example well known to the spear fishermen of ancient civilisations who went hungry until they learned to aim their spears off target’. The Sun is also sufficiently distant from the Earth – 149 591 000 km -that its rays can be considered to be parallel on arrival and of equal intensity over short, terrestrial distances. The same, of course, is not true of room lights – an example of a class of lights called ‘omnilights’ – which emit light radially in all directions, with an intensity which falls off with the square of the distance between light source and object illuminated. Dramatic effects can be created in graphics using light from simulated spotlights, which are directional and of variable intensity.

When light strikes the surface of an object, part of the light is turned back from the surface by reflection. The remainder of the light is transmitted into (absorption) or through the material (transmission). If the surface of the object is smooth, then the angle of reflection equals the angle of incidence (specular reflection). If the surface is rough, the reflected light goes off in all directions (diffuse reflection).

Shade and shadow can be thought of as the inverse of light. The surface of an object which is turned away from direct light, receiving only light reflected from other surfaces, is said to be shaded. A shadow occurs when an opaque object prevents light from reaching a surface which would otherwise be illuminated. In the real world, objects are illuminated by direct sunlight, by light reflected from neighbouring objects and by light scattered from dust and other particles present in the atmosphere, producing complex results which are not easy to predict. The summation of all these sources of background lighting is commonly called ‘ambient’ light. Before creating graphics which attempt to simulate real life lighted scenes, a careful study of photographs can be a source of useful guidance.

Examples of the use of diredional lighting

Light’s electromagnetic waves can ‘interface’ with each other in the same way as do the ripples from two stones thrown into a pond. When two ripples are in phase they interfere additively, reinforcing each other; when they are out of phase, they interfere destructively, cancelling each other out. It is this phenomenon which is responsible for the colours seen in soap bubbles. The light waves which reflect off the inner surface of the bubble’s soap film interfere with light waves of the same wavelength which reflect off the outer surface of the film. Some of the wavelengths interfere constructively, so that their colours appear bright, while others interfere destructively, so that their colours are not seen. The same effect causes the colours seen in films of oil on the surface of water. In graphic design, incorrect alignment of the halftone screens used for printing the four process colours can cause undesirable interference between the reflected colours – the moire effect – but the interference principle can also be exploited positively by overlaying coloured grids to produce interesting effects.

Light Sources and The Artist

As life took hold and evolved on Earth, our earliest cave-dwelling ancestors apparently discovered that fire, as well as offering some deterrent to passing predators, provided enough light to paint by, albeit a flickering reddish light, as the spectral output from the relatively low temperature of a wood fire peaks in the red part of the spectrum. Centuries later, artists and sculptors worked by the light of torches made from dried rushes or resinous wood, oil lamps and then candles (beeswax candles were used in Egypt and Crete as early as 3000 BC). The term ‘candlepower’ was coined to provide a benchmark against which to measure the ability of other sources to give off light and was based on the light emitted by a standard candle. It was not until the early nineteenth century that gas was used to provide street, factory and then domestic lighting, with its characteristic blue glow. The first gas burners were simple iron or brass pipes with perforated tips, but development of the gas mantle, impregnated with cerium and thorium compounds, which became incandescent when heated by the gas flame, produced a much whiter light.

Moiré effect

In 1879, Thomas Edison developed a successful carbon filament lamp which evolved into the ubiquitous light bulb, employing a tungsten alloy filament heated to an incandescent 3000 °C. Although operating at a lower temperature than the Sun (the wavelengths emitted by the Sun are close to those of the radiation emitted by a heated source – called a black body source – at a temperature of 5500 °C), the light bulb emits wavelengths across the whole visible spectrum. Today, of course, the common light bulb is being replaced more and more by lighting based on gas discharge technology. Many football matches are now watched in the blue/white light cast by clusters of high intensity arc lights, while motorway interchanges are illuminated by the rather sickly yellow/orange glow of sodium lights. As well as its lower running costs, fluorescent lighting is generally whiter than that of ordinary light bulbs, as its equivalent black body temperature of 4100 °C is closer to that of the Sun. The interiors of fluorescent lamps are coated with phosphors which glow when excited by cathode rays. The phosphors absorb the invisible but intense ultraviolet components of the primary light source and emit visible light. In fact, if the chemicals in the interior phosphor coating are varied, different light tones – such as the ‘plant light’ which mimics sunlight – can be produced.

Best known to the public through spectacular Tight shows’, the relatively recently discovered laser (light amplification by stimulated emission of radiation) is a device which amplifies light and produces coherent light beams (beams with a single wavelength), ranging from infrared to ultraviolet. Laser light can be made extremely intense and highly directional.

The interior lighting conditions experienced (endured is perhaps a more accurate description) by artists over the centuries is reflected in the sombre, even gloomy, nature of much of their work, but their appreciation of the nature and importance of light is also evident in examples such as Gustave Dore’s Opium Smoking and, of course, in the work of artists like Constable and Turner who produced remarkable works depicting the effects of light and atmosphere. For Claude Monet, the prime exponent of Impressionism, the world was composed not of objects but of a dazzling display of light reflected from those objects, while Georges Seurat even attempted to render scientifically the impressionist perception of light with the use of small dabs or dots of paint in the style which became known as Pointillism. Those who have visited Provence, in the south of France, will also understand why the extraordinary interaction between light and landscape in that region had a compelling attraction for the Impressionists.

The discovery of the photographic process was to prove an important milestone in the understanding and application of light in the design process, directly influencing the work of artists like Degas, who painted subjects in movement, as though captured by a camera lens. Photographers quickly discovered how the manipulation of the lights used to illuminate a scene could dramatically alter the appearance of the final image. As the technology evolved, the mobility of the camera also allowed the photographer to explore and capture conditions of light and shade which were denied to his fellow artists.

Pointillism

Sight

The Eye

Eyes are as varied as the animals which possess them. The eyes of the myriad species which inhabit the planet vary from simple structures capable only of differentiating between light and dark, to complex organs, such as those of humans and other mammals, which can distinguish minute variations of shape, colour, brightness, and distance.

Human vision has the widest colour gamut, that is the widest range of visible colour. It also has the widest dynamic range, capable of discerning gradation in shadow that is one millionth the brightness of the highlights in the field of view.

The Psychology of Visual Perception

Sight – perhaps the most miraculous of the senses, which we sadly tend to take for granted – is a process which in fact takes place in the brain, not in the eye. The amount of light entering the eye is controlled by the pupil, which has the ability to dilate and contract. The cornea and lens, the shape of which is adjusted by the ciliary body, focus the light on to the retina, where receptors convert it into nerve signals which pass to the brain. The function of the eye, therefore, is to translate the electromagnetic vibrations of light into packets of nerve impulses which are transmitted to the brain for interpretation. The retina consists of approximately 130 million light-sensitive cells, which are either cone shaped or rod shaped. The cone-shaped cells respond to colour, and it is believed that the cones are distributed evenly to react to one of the red, green, or blue light primaries. As a sensation experienced by humans and some animals, perception of the colour of the light wavelengths so received is a complex neurophysiological process. Among mammals, only humans, primates, and a few other species can recognise colours.

Perceptual psychologists believe that, once the nerve impulses have been received and an object has been perceived as an identifiable entity, it tends to be seen as a stable object having permanent characteristics, despite variations in its illumination, the position from which it is viewed, or the distance at which it appears. Thus, an individual viewing a new scene interprets it by synthesising past experience with sensory cues present in the new scene – using depth cues such as linear perspective, partial concealment of a far object by a near one or the presence of aerial perspective ‘haze’. Fortunately for the graphic designer, however, the brain can be deceived! Indeed, this deception is the very basis of much graphic design. For example, it is because the brain is conditioned to associate the converging lines and shaded faces of a building with its three-dimensional depth, that, by drawing the building using converging lines and shaded surfaces on a two-dimensional surface, we trick the brain into seeing the drawing as having three dimensions.

Such illusions are of great practical importance in environmental and architectural design and in the theatre, as a means of creating a sense of depth and space in a confined area. The concept has also been carried over to the design of the desktop PC GUI (Graphic User Interface) where subtle shading of buttons on a flat computer screen creates a powerful 3D illusion – which is further reinforced when we click the button and the shading alters in the way that our brain is conditioned to expect. To learn more about graphic illusion, the reader is advised to study the work of the Dutch graphic artist Maurits Corneille Escher (1898-1972) who devoted his life to the creation of an intriguing world of impossible perspectives, optical paradoxes and visual puns.

Illusions are believed to result from the erroneous application of learned depth or colour cues and can occur in nature. I remember well, during a cycling holiday in Ayrshire in Scotland, coming across a famous (but unknown to me) stretch of road called the Heely Brae. As all my senses told me that the road was on a downward incline, I sat back in the saddle, expecting to freewheel down the slope. Instead, I found that I quickly came to a stop and had to resume pedalling in order to reach the bottom! The illusion was created by an unusual relationship between the contours of the adjoining hills and hedgerows.

Illusions are also common in colour perception, notably in the phenomenon called ‘simultaneous contrast’, in which the appearance of a particular area of colour is greatly altered by changes in its surroundings. This effect is of practical importance in fashion and textile design as well as in graphic design. The relationship of text colour to background colour is also important to ensure legibility. The colour of ambient lighting can also have a significant effect on the way we perceive colour; many readers will have experienced the mysterious change in colour undergone by a sweater wrapped under the fluorescent lights of a store and later unwrapped in daylight!

The legibility of text depends crucially on the relative colours of text and background

As individuals, not only do we vary in our description of colour, but our perception of colour is influenced by experiences, memory, and even, research tells us, by the use of hallucinogenic drugs. Research has also shown that certain colours and types of lighting can effect us subliminally. We describe some colours as ‘slimming’ and some lighting as ‘flattering’. We are apparently soothed by a green environment and excited by red, but feel welcomed by a combination of red and yellow, as patrons of MacDonald’s will know.

For average members of the population, differences in how we perceive colours don’t seriously affect our lives. In some members of the population, however, defects in the retina or in other nerve portions of the eye can cause colour blindness. Dichromatism – partial colour blindness – is manifested by the inability to differentiate between the reds and the greens or to perceive either reds or greens. Dichromatism is a hereditary condition which affects as many as seven percent of the male population, but a much lower percentage of females. In the realm of commercial printing, differences in colour perception may determine the success or failure of a print job. Being aware of how different factors influence colour perception and determine the appearance of printed colours will maximise the probability of success.

Stereoscopy and the Cone of Vision

The fact that nature endowed us with two eyes, which are separated by a few centimetres, means that the objects we view appear slightly different to each eye; this effect provides a sense of depth and can be used, in graphic design, to produce stereoscopic three-dimensional images on a two-dimensional surface.

Experimentation has shown that, if we view a scene with the eyes at rest, then our field of view is defined by a cone -our ‘cone of vision’ – of angle approximately 60°. This field of view can be thought of as analogous to that seen through the viewfinder of a camera. A camera’s angle of view – the amount of the field that the lens will ‘see’ – depends on the lens’s focal length. The field of a camera lens may be as small as 15° or as large as 140°. A standard lens covers around 60°, a wide-angle lens 90° and a telephoto lens 30°. A wide-angle lens forms an image with a wide field of view, but causes the scene to appear smaller and more distant than it actually is. Such a lens could be used, for example, to take a close-up of a tall building, but would introduce considerable distortion, especially at the edges of the picture. A wide-angle photograph of a person with hands reaching out would make the hands appear disproportionately large. Therefore, when creating graphics depicting objects or scenes as they would normally appear in perspective in the real world, it is important to ensure that the objects or scenes fall within the 60° cone unless the objective of the graphic is to create effects similar to those produced by special camera lenses such as the wide-angle or fisheye lenses.

Perspective

As children grow up, observing and interacting with their surroundings, the rules of perspective are learned intuitively, helping the children to understand the world around them. Those of them who choose to become graphic designers, however, need to learn how to translate these three-dimensional rules on to a two-dimensional surface, if convincing results are to be achieved.

Rule 1 Convergence

As parallel lines recede into the distance, they appear to converge at a constant rate.

Rule 2 Foreshortening

Equally spaced objects appear to become closer together, at a constant rate, as the distance from the observer increases.

Rule 3 Diminution

Equal sized objects appear to become smaller, at a constant rate, as the distance from the observer increases.

In addition to being aware of these three rules, the designer of three-dimensional scenes must allow for aerial perspective – whereby atmospheric effects cause distant objects to appear fainter than objects close to the viewer.

Colour

Colour is, of course, simply the way we describe light of different wavelengths. When we see colour, we are really seeing light. When we look around us, the light which enters our eyes does so in three ways – directly, e.g. from a light source such as the Sun or a light bulb, indirectly, by reflection from any smooth reflective surface, or by transmission through a transparent material, such as coloured glass. When we look at an object, the colour it appears to have depends on which wavelengths of the light falling on it are absorbed, reflected or transmitted. A yellow flower is yellow because it reflects yellow light and absorbs other wavelengths. The red glass of a stained glass window is red because it transmits red light and absorbs other wavelengths. The process by which we perceive the colours of natural objects around us can therefore be described as a ‘subtractive’ process. Subtractive, because the objects ‘subtract’ certain wavelengths from the white light falling upon them before reflecting and/ or transmitting the wavelengths which determine their colour. The colours we see when we look at an original old master depend on the optical properties of the pigments used to produce the original paint employed by the artist and on how these properties may have altered over the centuries since the work was created.

Some of the earliest cave drawings were created using charcoal from burnt sticks mixed with a natural binder such as animal fat, fish glue or the sap from plants, or using natural chalks – white calcium carbonate, red iron oxide or black carboniferous shale. The first ‘paint’ used by the earliest cave painters was a crude rust-coloured paste made from ground-up iron oxide mixed with a binder.

Colour was introduced to early three-dimensional works of art by applying coloured pieces of glass, stone, ceramics, marble, terracotta, mother-of-pearl, and enamels. Although mosaic decoration was mainly confined to floors, walls and ceilings, its use extended to sculptures, panels, and other objects. Tesserae – shaped pieces in the form of small cubes -were embedded in plaster, cement, or putty to hold them in place.

By the time of the Ancient Egyptians, the artist’s palette of colours had expanded to include pigments predominantly made from mineral ores – azurite (blue), malachite (green), orpiment and realgar (yellow), cinnabar (red), blue frit and white lead. Additional pearly or pastel-like colours offered by gouache – a form of watercolour which uses opaque pigments rather than the usual transparent water-colour pigments – were also developed by the Egyptians. The wall paintings of ancient Egypt and the Mycenaean period in Greece are believed to have been executed in tempera – a method of painting in which the pigments were carried in a medium of egg yolk. The Romans added to the palette the blue-purple organic pigment indigo, extracted from the Indigo plant, as well as Tyrian purple and the green copper oxide, verdigris. Many years later, the thirteenth century saw the introduction of lead tin yellow, madder (red), ultramarine (blue green) and vermilion (red).

In contrast to the older water-based media, such as fresco, tempera and watercolour, oil paints, developed in Europe in the late Middle Ages, consist of pigments ground up in an oil which dries on exposure to air. The oil is usually linseed but may be poppy or walnut. In the late eighteenth century the Industrial Revolution boosted the palette with chromes, cadmiums and cobalts, but it was not until the following century that paint consisting of prepared mixtures of pigments and binders became commercially available on a wide scale.

In parallel with the gradual evolution of the types and colours of paint available to the artist, inks used for printing also evolved. Lampblack- a black pigment produced by the incomplete burning of hydrocarbons – was in use in China as early as AD 400.

For many centuries, black was the accepted colour for woodblock printing, with decorative colour being added by quill pen. Early letterpress printing used inks composed of varnish, linseed oil, and carbon black. In the eighteenth century the first coloured inks were developed and in the nineteenth century a wide variety of pigments were developed for use in the manufacture of these inks. Manufacture of modern printing inks is a complicated process often using chemically produced rather than natural pigments and containing as many as fifteen separate ingredients, including modifiers or additives and dryers which control appearance, durability and drying time.

Simple Colour Models

Although the spectrum contains a continuous range of visible colours, it can be broken down into three colour ‘regions’ – red (and its neighbouring colours), green and its neighbours, and blue and its neighbours – each region representing one-third of the visible spectrum. Conversely, when colours within these same three regions are projected on top of one another, white light is recreated. Early optical experiments also showed that if only two of the three regions overlapped, a totally different colour was created – red and green producing yellow; red and blue producing magenta; green and blue producing cyan. Because the red, green and blue combine to produce white light, they became known as additive primaries. Because the yellow, magenta and cyan were formed by taking away, or subtracting, one of the three additive primaries, they were called subtractive primaries. The figure below right summarises the interaction of the subtractive primaries. The two figures are crude colour ‘models’ – methods of representing the relationship of primary colours within the spectrum.

Additive colourmodel

subtractive colourmodel

The colour wheel is a more helpful model, displaying the compositional relationships between the spectral colours. Mixing any two of the primaries produces a ‘secondary’ colour which appears midway between them on the wheel. Further subdivisions can be created by continuing to mix adjacent colours. Opposite colours on the wheel are complementary; placed side to side, they produce a harmonious result, but mixed together, they effectively cancel out. A number of pairs of pure complementary spectral colours also exist; if mixed additively, these will produce the same sensation as white light. Among these pairs are certain yellows and blues, greens and blues, reds and greens, and greens and violets.

Colour wheel

As well as describing colour in terms of the visible spectrum, it can be described in terms of three characteristics -hue, lightness, and saturation. Hue is the name of the colour, such as red or orange; lightness (sometimes called value) indicates the darkness or lightness of a hue – in other words, how close it is to black or white; saturation (also called chroma) refers to the spectral purity of the hue, described using terms like vividness or dullness. The figure on the right shows a representation of the three variables. Hue is represented by angular position around the circle; saturation increases radially from the centre of the circle outwards; lightness, or value, is represented by positions along the vertical scroll bar.

HLS model

Tints, Shades and Tones

The relationship between tints, shades and tones is best explained by reference to the HLS model. The hue values range from 1° to 360° – equivalent to settings on a colour wheel – where 0° is the same as 360°. The hue values for primary colours are red (0°), yellow (60°), green (120°), cyan (180°), blue (240°), and magenta (300°). The standard setting for a hue is 50% lightness and 100% saturation. If, for example, pure red (R255, GO, B0) is highlighted in the palette, the HLS values display hue 0°, lightness 50%, and saturation 100%.

The hue setting selects a starting colour value. Varying the lightness value adds a percentage of white or black to the hue. Increasing lightness adds white, producing a ‘tint’ of the selected colour; decreasing lightness adds black, producing a ‘shade’ of the selected colour.

A pure colour has a saturation value of 100%. Decreasing saturation, while keeping lightness constant, adds grey to the colour, reducing its purity and producing a ‘tone’ of the colour. A continuous tone image – e.g. a colour photograph – is one in which colours and shades flow continuously from one to another.

The relationship between tints, shades and tones can be summarised in a colour triangle. Tints offer the designer a range of subtly different variations around a single colour in one pass though an offset press, while two colour printing extends the possible variations to shades and tones. Varying the brightness and saturation of object surfaces within a graphic design also provides a simple means of creating the illusion of depth or distance