PhotographyTips.com - the #1 guide to better conventional and digital photography Become a Member iPhone Posing GuideGuide to Posing the Female Model BookGuide to Posing the Model CD
Search
Login

Member Login

Find us on Facebook
Follow us on Twitter
Find us on Flickr
Connect with us on LinkedIn

SPONSORS

Sell Photos Online

FEATURED SITES


How light behaves


Low cloud or mist will diffuse and scatter the sun's rays, sometimes providing spectacular effects.
Low cloud or mist will diffuse and scatter the sun's rays, sometimes providing spectacular effects.

Light, whatever its source, moves out in straight lines and spreads out over a larger and larger area as it travels, much the same as ripples in a pond after throwing in a rock. When light strikes an object, it is either absorbed or scattered. Some frequencies are absorbed more than others – this is what gives objects their colors. White surfaces scatter all colors equally, while black surfaces absorb all light.

WAYS IN WHICH LIGHT BEHAVES

Light can be

  • reflected,
  • scattered,
  • transmitted,
  • diffused,
  • refracted,
  • diffracted,
  • polarized or
  • absorbed.


Reflected light

Light travels in a straight line until it meets an object that alters its course. When it strikes a smooth flat surface, such as a mirror or the calm surface of water, it bounces like a ball off of it at the same angle with which it struck the surface. The reflected light waves remain in the same order as they were when they approached the surface. This is why objects we see in a mirror remain clearly defined.

All objects reflect light. In fact, it is this reflected light that we see and photograph (unless the object produces its own light), not the object itself.

There are three types of reflected light. It can be:
(1) diffuse, reflecting with uniform brightness regardless of the observer’s position,
(2) direct (also known as “specular”), reflecting off a mirror-like surface and visible only by an observer who is directly in the path of the reflection, and
(3) glare, which is also a direct reflection, but is polarized.
Most surfaces will reflect light in all three ways to varying degrees.

The light reflected from the surface of the ocean is almost blindingly bright, although not as bright as the source - the sun itself - since some of its reflection is broken up and scattered by the irregular surface.
The light reflected from the surface of the ocean is almost blindingly bright, although not as bright as the source - the sun itself - since some of its reflection is broken up and scattered by the irregular surface.

This image by photographer Karen Meeks shows light's diversity, from flare to glare, from reflected light to deep shadow.
This image by photographer Karen Meeks shows light's diversity, from flare to glare, from reflected light to deep shadow.

Scattered light

When the surface that is struck by light is rough, the light waves reflect off it at different angles, scattering widely in all directions. Once it is scattered, the light becomes diffused in character.

Light emanating from a prism in the colors of the spectrum is also known as scattered light. A single white light beam is evenly scattered into its colored components.

Transmitted light

There are two kinds of light transmission - direct and diffused.

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.


Diffused light

Light will also pass through translucent materials - i.e. materials that permit light to pass through but that also diffuse it so that persons or objects on the other side are not clearly visible or not visible at all. Frosted glass or onion skin paper are examples of translucent materials. Photo studios commonly use translucent material between the studio lights and the subject being photographed to diffuse the light.

The largest example we have of diffused light is the sky itself. Its diffused light is caused by light striking and becoming scattered by 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 color of the sky. (See our section entitled Atmosphere and sunlight to learn why the sky turns red at sunset.)

Light from studio flash is directly transmitted, giving predictable results for the studio photographer, as in this publicity picture of renowned singer/songwriter, Laura Jean Hogan.
Light from studio flash is directly transmitted, giving predictable results for the studio photographer, as in this publicity picture of renowned singer/songwriter, Laura Jean Hogan.

Water reflects, scatters, transmits, refracts, absorbs and diffuses light.
Water reflects, scatters, transmits, refracts, absorbs and diffuses light.

Refracted light

Refraction is a change of direction of a ray of light. 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 (see "How fast does light travel?" below), 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.

Diffracted light

Diffracted light is a phenomenon exhibited by a light’s wave front when passing the edge of an opaque object (one that does not allow light to pass through it). The light becomes modulated, causing a redistribution of the light’s energy within the wave front. You will see it at the edges of the object’s shadow, in the form of minute dark and light bands. The edges of the shadow have a fuzzy appearance. Think of ripples meeting a rock in a pond or a twig in a stream, as in the picture at the top of this page. They go around the twig in a new series of ripples that can be seen on the sides of the twig. Light waves behaving in a similar manner are said to be diffracted.

Polarized light

Light waves from the sun undulate at all angles, which means sunlight is unpolarized. A polarizing filter (simply called a polarizer) can polarize sunlight, making its waves undulate at one angle. When properly used, this filter almost totally eliminates glare and reflections from glass.


Absorbed light

When light is neither reflected, dispersed nor transmitted by an object, it is absorbed by it.

All materials actually absorb some light in varying amounts. If they didn’t, we would not see things in color. A leaf, for instance, is green because it absorbs red and blue wavelengths and reflects green. Technically-speaking, the colors of most objects are not their true colors. They are instead the colors of light wavelengths that they reflect. Place these objects under a different type of light, and their colors may appear to change, dependent upon how much of that light they absorb and reflect.

Absorbed light disappears as visible light, but its energy continues to exist, having been transformed by absorption, usually into heat. A black shirt absorbs sunlight, and the heat created can be felt by the person wearing the shirt more so than a person wearing a white shirt, which reflects all light.

HOW FAST DOES LIGHT TRAVEL?

The speed of light, like the speed of just about anything, depends upon the substance it is travelling through. It is fastest when travelling through nothing - i.e. a vacuum.

Today's precise measurements give us the speed of light in a vacuum as 186,282.396 miles per second, which most people round out to 186,000 miles per second so it is easier to remember. Metrically speaking, light travels at just under 300,000 kilometres per second - 299,792,458 meters per second to be exact.

The velocity of light in air varies slightly, averaging about 3 per cent less than in a vacuum. Traveling through water, light’s speed is about 25 per cent less and 33 per cent less through glass.

The fruit and foliage are green because the plants absorbs red and blue wavelengths, and reflects green.
The fruit and foliage are green because the plants absorbs red and blue wavelengths, and reflects green.