The Nature of Light
Written by Abin Alex and Anu Joseph.
Abstract
A practical guide to the nature of light: what light is, why it has colour, how photographers describe it by brightness, colour and contrast, colour temperature in Kelvin, the four questions to ask any light and how light travels, with two diagrams and two tables.
Keywords: nature of light, what is light, electromagnetic spectrum, colour temperature, Kelvin, brightness, contrast of light, photons
What is light?
Short answer. Light is electromagnetic energy carried by photons, and it is what every photograph is made from.
- Light is energy, a form of electromagnetic radiation that moves through space in tiny packets called photons (Hunter and Fuqua, 1997, p. 10). Every photograph starts when light leaves a source and ends when light from a print or screen reaches someone's eye. Everything in between is the photographer shaping that light.
- Each photon carries an electromagnetic field that rises and falls as it moves. Every photon travels at the same speed, but in some the field rises and falls faster than in others (Hunter and Fuqua, 1997, pp. 11-12).
- Light is a form of energy, and an object that is heated gains energy and then tries to give it off. One way to give off energy is to emit light. A hot object gives off light of high energy and short wavelength. A cold object gives off a longer wavelength. As the wavelength falls, the energy rises.
Switch on a lamp in a dark room and note what you can and cannot see. You see light and what it lands on, never the light travelling.
A film is made of light, so every lighting decision is a decision about energy reaching the sensor.
Cham tipYou never see objects. You see the light that comes back from them.
Cham taskWrite in three lines what light is, what a photon is and why a hot object glows.
Check yourself: What is light?
Electromagnetic energy that travels as photons.
Why does light have colour?
Short answer. Colour is the effect we see when the frequency of the light changes, and visible light is a narrow part of the spectrum.
- How fast the field rises and falls is its frequency, measured in hertz. Photons with more energy have a higher frequency, and our eyes read that difference as colour. Red carries less energy than blue, and its field cycles at only about two thirds of blue's rate (Hunter and Fuqua, 1997, p. 12).
- Visible light is one narrow band of the electromagnetic spectrum, between infrared and ultraviolet (Figure 1). Film and sensors can respond to a wider range than the eye, which is why ultraviolet light the eye cannot see can still degrade a picture (Hunter and Fuqua, 1997, p. 13).
Look at a prism or a CD in sunlight. Name the colours in order from red to blue.
Colour on screen is a choice of frequency mix. A warm scene leans red and a cold scene leans blue.
Cham tipMore energy means faster field and bluer light.
Cham taskDraw the spectrum from radio to x-rays and mark the visible band.
Check yourself: What does the eye see when the frequency of light changes?
A change in colour.
How do photographers describe light?
Short answer. By brightness, colour and contrast.
- Photographers are mainly concerned with the brightness, colour and contrast of light (Hunter and Fuqua, 1997, p. 13). Describing the light is the first step to controlling it, and when you cannot control it, as in landscape and architecture, describing it tells you whether to shoot or to wait.
- Of the three, brightness comes first. Too little light and there is no picture at all. More than the minimum gives you choices: a smaller aperture for depth, a faster shutter to stop movement, or a lower ISO for a cleaner file.
- Contrast, as the book uses the word, is about the angle of the rays. A light has high contrast if its rays strike the subject from nearly the same angle, and low contrast if they strike from many different angles (Hunter and Fuqua, 1997, p. 15). We call this the quality of light, hard or soft, and it has its own guide.
- The contrast of the light is only one influence on the contrast of a photograph. Subject matter, composition and exposure also change it.
Look at a scene and say its brightness, colour and contrast out loud before you raise the camera.
A cinematographer reads a location in the same three words before choosing lights and lenses.
Cham tipBrightness first. A brighter light is almost always a better light.
Cham taskDescribe three different lights, a window, a bulb and the sun, in brightness, colour and contrast.
Check yourself: What three qualities of light do photographers describe?
Brightness, colour and contrast.
What is colour temperature?
Short answer. The colour of a glow depends on how hot it is. Low Kelvin is warm and orange, high Kelvin is cool and blue.
- Photographers call light white when it has a roughly even mix of red, green and blue (Hunter and Fuqua, 1997, p. 14). The mix can vary a great deal and the brain still calls it white, but film and sensors do not adjust automatically, so the colour of different white lights has to be measured.
- The measure is colour temperature in Kelvin, borrowed from physicists. Heat a material hot enough and it glows, and the colour of the glow depends on the heat. A light of high colour temperature has a lot of blue in it, and a low one leans to red and yellow (Hunter and Fuqua, 1997, p. 15).
- A piece of iron in a fire first goes dull red, then reddish yellow and then white, as hotter means shorter waves and higher energy (Grey, 2004, p. 11). A tungsten bulb glows at about 3200K, the reddish yellow stage. Midday sun is about 5500K and open shade can reach 8000K (Figure 2). Low Kelvin is warm orange and high Kelvin is cool blue, and this is the basis of white balance.
- The three standards photographers use are 5500K daylight and two tungsten standards, 3200K and 3400K. Table 1 lists them.
- A colour temperature meter outdoors on a perfectly clear day can read 10,000K or more, which is why skin sometimes looks pasty in that light (Grey, 2004, p. 11). Not every white light has a continuous spectrum: most fluorescent tubes leave a green cast that is hard to correct (Child and Galer, 2008, p. 12).
| Source | Kelvin | Look |
|---|---|---|
| Red to yellow light | About 2000K | Warm, red and yellow |
| Tungsten bulb | 3200K or 3400K | Warm, reddish yellow |
| Midday sun, daylight standard | 5500K | White, neutral |
| Open shade | About 8000K | Cool, bluish |
| Very blue light | About 10000K | Cool, a lot of blue |
Table 1. Common colour temperatures.
Photograph the same white card under a bulb, in sun and in shade. Compare the colour of the card.
Tungsten and daylight lights are the two standards on a set, and gels are used to match one to the other.
Cham tipLow Kelvin looks warm. High Kelvin looks cool.
Cham taskShoot a white card under three lights and write the Kelvin of each.
Check yourself: Which is warmer, 3200K or 5500K?
3200K.
What four questions describe any light?
Short answer. Intensity, direction, quality and colour.
- Every light, whether sun, window, bulb or flash, can be described by four questions (Child and Galer, 2008, p. 11). Ask them before each frame. Table 2 sets them out.
- The book describes light as brightness, colour and contrast. The brightness is our intensity, and the contrast is what we call quality.
| Property | Question | Read it from |
|---|---|---|
| Intensity | How much light? | The meter and the exposure |
| Direction | Where does it come from? | Where the shadows fall |
| Quality | Hard or soft? | The edge of the shadow |
| Colour | Warm or cool? | The Kelvin and the white balance |
Table 2. The four questions to ask any light.
Pick any light in the room and answer all four questions in one sentence.
A lighting plan on a set answers the same four questions for each light.
Cham tipRead direction from shadows and quality from the shadow edge.
Cham taskDescribe a window light with the four questions.
Check yourself: What are the four properties of light?
Intensity, direction, quality and colour.
How does light travel?
Short answer. Light travels in a straight line until something reflects or scatters it, and opaque objects cast shadows.
- Light travels in a straight line, or until it is reflected or scattered by objects in its path.
- Opaque materials do not let light through. We cannot see through them, and we see only the surface because light is sent back from it to our eyes. A shadow forms where an opaque object blocks the source from an area. Shadows are darker, but some light always reaches them, and we can still see the colour of a shadowed object even when it is very dark.
Hold a card in front of a lamp and look at the shadow. Note that the edge is straight.
Because light is straight, a flag placed between a light and the lens always works.
Cham tipIf you can draw a straight line from source to subject, light reaches it.
Cham taskDraw the path of light from a lamp to a card and the shadow behind it.
Check yourself: What path does light follow?
A straight line until it is reflected or scattered.
Questions beginners ask
What is light?
Light is electromagnetic energy that travels in photons. It is the raw material of photography.
Why does light have colour?
Colour is what we see when the frequency of the light changes. Red has a slower field than blue.
What is colour temperature?
The colour of a glowing source measured in Kelvin. Low Kelvin is warm and orange, high Kelvin is cool and blue.
What Kelvin is daylight?
Daylight is about 5500K, tungsten is 3200K or 3400K and open shade is about 8000K.
What four questions describe a light?
Intensity, direction, quality and colour.
References
- Child, J. and Galer, M. (2008) Photographic lighting: essential skills. 4th edn. Oxford: Focal Press.
- Grey, C. (2004) Master lighting guide for portrait photographers. Buffalo, NY: Amherst Media.
- Hunter, F. and Fuqua, P. (1997) Light: science and magic: an introduction to photographic lighting. 2nd edn. Boston: Focal Press.
Further reading
- Hirsch, R. (2008) Light and lens: photography in the digital age. Burlington, MA: Focal Press.
- Langford, M. and Bilissi, E. (2011) Langford's advanced photography. 8th edn. Oxford: Focal Press.
- Marr, D. (2004) Beginner's guide to photographic lighting: techniques for success in the studio or on location. Buffalo, NY: Amherst Media.
How to cite this guide. Alex, A., & Joseph, A. (2026). The nature of light: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/nature-of-light/
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