Mastering Light In Photography: What is Light?

Photography depends on light. However primitive or sophisticated your photography equipment, from a home-made pinhole camera to your smartphone, it cannot create an image without light. Each time that you press your camera’s shutter you are recording light onto a sensor or piece of film which results in an image. This makes light one of the pillars of photography.

Image of the original illustration from the “Elementary Treatise on Physics” by Ganot’s published by E. Atkinson in 1872.

In this article we discuss what light is and how it naturally behaves.

This is part one of our four-part article series on understanding light. You can find the rest of the series here:

Contents

  1. What is Light?
  2. How Does Light Behave?
    • A. Reflected Light
    • B. Transmitted Light
    • C. Absorbed Light

What is Light?

People have tried to comprehend and define light since the beginning of human intelligence. Two of the greatest minds to wonder about the nature of light were active at roughly the same time and came up with apparently conflicting theories as to what light might be:

  1. British mathematician and physicist, Sir Isaac Newton (1643 -1727), postulated that light is an emission of tiny particles.
  2. Dutch astronomer, physicist and mathematician Christiaan Huygens (1629-95) developed a wave theory of light.

Both had data and scientific observations to back their theory. Using their own theory as a basis, each went on to other discoveries and inventions that would not have held true if their theory had been incorrect.

If one was right, the other had to be wrong, didn’t they? Could light be both energy and matter, wave and particle?

The answer is yes. Modern science allows that both theories are substantially accurate. Some experiments in quantum theory have light behaving as a wave. In others, light seems to take on all the characteristics of a particle. Light can be considered as both energy and matter.

Pictured here is the first ever photograph of light behaving as both a particle and wave simultaneously. Image by Fabrizio Carbone/EPFL 2015. For more information on this research please follow this link.

In the majority of light’s relevance to photography, light can be described as acting like a wave, as energy—not matter—that can spread, bend and react with obstacles just like waves in water. Most of our study of light in this section will refer to light waves rather than to photons.

How Does Light Behave?

Light moves in predictable straight lines that spread out over a larger and larger area as it travels. This is much the same as ripples in a pond after throwing in a rock. Light travels in this way until it meets an object that alters its course.

When light strikes an object, it is either:

  • reflected,
  • transmitted,
  • or absorbed.

In many cases, light will behave in all three ways when it strikes a surface. The degree of which depends on the surface’s properties.

Reflection, transmission, and absorption form the foundation for a photographer in understanding how to manipulate and use light as a tool.

Reflected light

Unless you are taking an image of a light source itself, everything that you photograph is reflected light of some sort. Light travels and reflects off of the surfaces in our World and is absorbed by our retina, or in the case of photography—our camera sensor.

It should come as no surprise that light reflection also behaves in a predictable manner. The law of reflection states that the angle of the reflected ray is equal to the angle of the incident ray.

Incident light simply refers to the original light that comes from the light source. This could be the rays of the sun, a household light or a streetlamp. It is the light from any of these sources before it is altered.

In order to better understand the law of reflection, let’s first consider a mirror. If you direct a beam of light at the exact right angle of a mirror, it will bounce back in the same path of the traveling beam of light. What happens when you change that angle? Well, according to the law of reflection, the reflected light will always travel at an angle that is equal to that of the beam. If light is directed at a mirror from a 45 degree angle, it will reflect at a 45 degree angle.

Regular vs diffused: the two types of light reflection

The law of reflection is especially noticeable when light is reflected from a mirrored surface. However, most surfaces in our world are not perfect mirrors. What happens to light when it’s reflected from a rough surface?

Light reflection can be categorized in two distinct ways:

  1. Regular/Specular

A regular reflection will reflect almost all of the incident light uniformly and at a similar intensity. Highly reflective, smooth surfaces—such as a mirror, produce this type of reflection. When a beam of light is directed at a mirror, the reflected light will travel in a similarly uniform beam. This means that the reflected light will only be observed at the exact angle where it is reflected.

  1. Diffused

A diffused reflection reflects and scatters light in multiple directions with reduced intensity. This occurs when light is reflected off of a rough surface– which is anything other than a clear mirror-like surface. The degree of roughness determines how much light is scattered and how bright the reflected light is. Textures that are really rough may reflect light in a completely haphazard or non-apparent way.

Transmitted light

Light transmission occurs when light passes through an object without being fully reflected or absorbed. Transmission is rarely perfect. In fact, even when light passes through a clear pane of glass, the characteristics of light are being altered—even if it’s unnoticed by the naked eye.

Direct vs diffused: the two kinds of light transmission

  1. Direct

We all know that light travels through clear plate glass and other transparent materials, and comes out the other side pretty much unchanged. This light is “transmitted” through the glass, and this type of light transmission—where the light passes through without changing—is known as direct transmission. Direct transmission occurs only when light strikes the surface of the glass head on, that is, at a perpendicular angle. The light will refract if it strikes the glass at any other angle.

  1. Diffused

Light will also pass through translucent materials. Frosted glass or tracing paper are examples of translucent materials. The most common example we have of diffused light is the sky itself. Its diffused light is caused by light striking and scattering due to molecules of air, dust and water in the atmosphere. Shorter wavelengths are affected more than longer ones. Since the wavelengths of blue light are not as long as those of the reds and yellows, blue light gets more scattered, causing the characteristic blue colour of the sky.

Refraction: Light can change course when passing through an object

Refraction is the bending of light that occurs when light passes from one medium to another caused by its change in speed.

Light bends when it strikes light-transmitting substances at any angle other than perpendicular. The density of the transmitting substance—for instance, glass or water—causes a change in the speed of the light, making it alter course to travel through the substance. It picks up its speed again as it leaves the substance, and therefore bends or refracts one more time.

Light refraction is the basis for lenses, magnifying glasses and even our eyesight.

Absorbed light

When light is neither reflected nor transmitted by an object, it is absorbed by it and is no longer visible

Absorbed light disappears as visible light, but its energy continues to exist. This is usually transformed into heat. A black shirt absorbs sunlight and the heat created can be felt by the person wearing the shirt. Whereas, a person wearing a white shirt will be cooler since it reflects all light.

Selective absorption or transmission gives objects their colour

All materials actually absorb some light in varying amounts. If they didn’t, we would not see things in colour. Some frequencies are absorbed more than others—this is what gives objects their colour. A leaf, for instance, is green because it absorbs red and blue wavelengths and reflects green.

This principle works the same for transmitted light. Certain wavelengths of light may pass through an object while some are absorbed. The frequency of light that is transmitted through the surface is the colour that our eyes or camera perceive. An orange glass bottle, for instance, absorbs every other colour frequency other than orange—which is transmitted through the glass.

Technically-speaking, the colours of most objects are not their “true” colours. They are instead the colours of light wavelengths that they reflect or transmit. Place these objects under a different type of light, and their colours may appear to change, dependent upon how much of that light they absorb. If you were to light a red apple under blue light, for instance, the apple would appear black. This is happening because the red apple absorbs all of the blue light and there is no red frequency for it to reflect.

Getting Started

Light is a complicated topic that deserves a thorough study as a photographer. It is, after all, the primary resource when creating images.

This article is part one in a four-part series that further explores light in photography. You can find the rest of the series here:

As you move forward in your photography, consider how important light is the photographic process. Try to notice light in your everyday life. Look for how it changes throughout the day and interacts with the different surfaces around you. This practice will strengthen your ability to use light without even using a camera.

Is there anything here that surprised you about light? Do you see light any differently now? Let us know in the comments below.

Leave a Reply

Your email address will not be published. Required fields are marked *