Understanding Light in Photography
The greatest composition will produce a poor image if the lighting is wrong. Bright or dull, hard or soft, sunlit or cloudy, sunrise or midday; all these give different light qualities that need to be used in the best way to generate the best images. In this first article I help you understand what light is, why it acts the way it does, why things don’t always come out the way you hope them to, and how the digital camera goes about controlling the colour of light under a range of lighting conditions.
What actually is light? The whole cosmos is enveloped in electromagnetic radiation, waves of energy, the great majority of which is invisible, though detectable with the right equipment. ER, as it’s often abbreviated to, ranges from very high energy, high frequency cosmic rays at one end of the spectrum through gamma and x-rays to very low energy, low frequency radio waves at the other end.
As we all know, some of this ER can be both dangerous and highly useful, whether X-rays in medicine or radio waves in telecommunications. In the middle of this vast electromagnetic spectrum sits visible light, that small segment of the ER spectrum that our eyes can see. Other well known forms of electromagnetic radiation include ultraviolet light, which sits just outside our vision at the high energy violet end of the visible spectrum, and infrared lying just outside our vision at the opposite, low energy red end. The electromagnetic spectrum.
The principal colours we recognize in the spectrum are red, orange, yellow, green, blue, indigo and violet. Each colour has a slightly different energy level, but much of the time all colours are present around us in varying balances. When there is an even mixture we have white light, which is roughly what we have during the middle of the day. The visible light spectrum.
We’ve all seen a rainbow, and this is one of nature’s best ways of showing how white light is made up of a mixture of different light colours. When rays of sunlight pass through water droplets suspended in the air, whether rain or spray, the water bends those rays. Each colour is bent by a slightly different amount, breaking the sun’s white light up into its component colours. We can only see this when our vision is directly in line with the direction of the light – i.e. with the sun right behind us. The result is the stunningly beautiful narrow, curving coloured band we call the rainbow. The order of the colours in a rainbow is always the same – red on the outside as it is bent the least by the raindrops, and violet on the inside as it is bent the most. A rainbow in front of Gullfoss Falls, Iceland.
We don’t need to have all colours of the rainbow present to make white light. Only three are needed, known as the primary colours: red, blue and green (quite different from pigments, such as paint and inks, where the primary colours are red, blue and yellow). All the other colours can be created by a blend of the three primary colours.
This is often represented diagrammatically by the colour triangle, with each primary at one of the triangle’s apices, the primaries blending to make the other colours along the triangle’s sides. A simplified drawing of the colour triangle.
Each primary has a complementary, or opposite colour: magenta for green, yellow for blue, and turquoise (also called cyan) for red. The presence of any of these complementary colours reduces the effect of their respective primary.
Their relationships can be represented in the colour triangle, each complementary sitting at the midpoint of each side, opposite each relevant primary. Alternatively, all six colours can be shown in a colour hexagon, with each occupying an apex. A knowledge of this is critical in photography using film, as filters often have to be fitted to the camera lens to correct for colour imbalances in the light.
With digital photography, however, the camera is usually set up to do this automatically with the photographer barely having to think about it. It is still useful to have an understanding of it, however, as doing so makes it easier to understand how to use the camera’s white balance settings (which are covered below).
Furthermore, a knowledge of primary and complementary colours is still crucial in two areas: studio lighting, and in-computer image manipulation, both areas where you are likely to want to fine tune colour balances. Simplified drawings of the colour triangle and the colour hexagon.
Everything in the world absorbs or reflects light of different colours to varying degrees, whether that light is coming directly or indirectly from the sun, or from an artificial light source.
When we look at any object and see its colour, that colour is the light that has not been absorbed by the object, but which instead has been bounced back, or – if the object is transparent – has been transmitted through it. A white shirt, for example, absorbs no light and so bounces every colour off it, making us perceive the shirt as white.
A black object, on the other hand, absorbs all light, bouncing nothing back and so appearing black. Vegetation absorbs all light colours reasonably well except green, which is bounced back for us to see, while a red dress reflects red light. A pane of glass will normally allow all light colours to pass through, thus appearing completely clear.
Coloured glass, on the other hand, contains material that will absorb all colours except the one(s) whose colour you want to see. Red glass, for example, absorbs all light except red, which can still pass through, enabling us to see the glass as red. This is true whether the glass is a huge window or a tiny lens filter. A plant leaf, reflecting green light but absorbing other light colours, appears green to us.
7 As already mentioned, light of different colours has different energy levels – blue and violet towards one end of the visible spectrum have a much higher energy than orange or red at the other end. This affects how much they’re absorbed or reflected by the objects all around us, ranging from dust suspended in the air to entire buildings, in that blue light is often readily bounced around, while red is more usually absorbed.
This is probably why the natural world appears largely blue and/or green – these are the main colours towards the high energy end of the spectrum, and are the colours most likely to be reflected off objects rather than absorbed. This is why a clear daytime sky is blue: it is filled with blue light being bounced around in the atmosphere on its way from the sun to us – it reaches us eventually (which is why we can see it), but via a very roundabout route.
Light reaching us directly from the sun appears white as it contains all the visible light colours (which is why during the day the sun, and the sky immediately around it, usually appear white). Blue sky is blue due to the presence of high levels of high energy visible light waves.
Under water, once you’re more than a couple of metres below the surface, everything appears blue. This is because all light at the red end of the spectrum is quickly absorbed by the water, and all that remains is blue or blue-green light. For this reason, underwater photographers always have to use flashguns – it’s not so much due to the lack of light but the need to correct the submarine colour imbalance by shining some white light onto the subject. A coral shows its true colours under water due to the use of flash gun.
9As I’ve already said, white light is created by an even mixture of the colours of the visible spectrum, notably of the three primary colours. This is the kind of light we experience in the middle of the day in clear weather. At other times of the day and in other weather conditions the colour balance can be rather different.
This is especially noticeable at sunrise and sunset, times when of course the sun is very low in the sky. At these times, the light coming from the sun towards us is shining almost parallel to the Earth’s surface, grazing along the surface and so passing through a very large amount of the atmosphere – far more than in the middle of the day when the sunlight hits our atmosphere much closer to 90 degrees and so comes down through the minimum amount of atmosphere.
The drawings above showing the angle of sunlight as it passes through the atmosphere in the middle of the day, and at sunrise or sunset.
As a result, at sunrise and sunset almost all the blue light is bounced by the atmosphere back into space and virtually the only light that reaches us directly from the sun is red light. A large proportion of this red light is absorbed as it passes through the atmosphere, but enough reaches us for the sun to be visible as a red ball, along with some red light in the sky or bouncing off nearby clouds.
The fact that we can see the sun as a red ball rather than a blinding fiery light – as it is in the middle of the day – indicates just how much of its output is either absorbed (red light) or bounced away (blue and green light) by the atmosphere. The more junk there is drifting around in the atmosphere, whether dust, water vapour or pollutants, the more light is absorbed or bounced away and the dimmer the sun’s red ball becomes.
The red light of sunrise, the only light passing directly through the atmosphere to the camera.
At dawn and dusk, when the sun is below the horizon (in other words, shortly before sunrise and shortly after sunset), no light reaches us directly from the sun. At this time the only light present is blue light reaching us very indirectly as it bounces its way through the atmosphere and eventually down to ground level. The result is the blue/violet lighting typical of twilight.
Any red present in the sky at this stage is due to sunlight shining from below our horizon ‘up’ into the sky immediately above the horizon, and then being bent just enough by atmospheric water vapour or dust for it to reach us, such as when it bounces off the bottom of high-level clouds.
A violet sky at dusk, resulting from the fact that the only light available at this time is highly indirect, deflected light.
What all this means for photography is that images shot during the first and last hour or two of the day will often be filled with a ‘warming’ rich red colour, something that is very moody and pleasing to the eye. Hence, much of our best photography – particularly landscapes – is taken at this time of day. Warm sunset sunlight reflecting off Atlantic cliffs.
As mentioned above for dawn and dusk, when we don’t receive direct sunlight one of the main sources of our light is indirect, light that has been bounced around in the atmosphere on its way from the sun to us. This inevitably is rich in blue.
Not only does this happen when the sun is below the horizon, but also – though to a much lesser extent – when it is high in the sky but unable to shine on us directly, either due to cloud cover or haze, or because we are in a shaded area.
Thus, on both a cloudy day and in sunny weather but in the shade the light will tend to be not truly white but rather rich in blue, something that usually makes images look less attractive, unless corrected (which will be covered below). A waterfall photographed in shadow on a sunny day, showing a strong bias towards blue light.
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