Principles of LightBeginning Photography

J. Hartney

• This is your eye. It's a ball with a hole in front. The hole is called your pupil. Light comes through the pupil and splashes inside your eye on the retina. Optic nerves carry information about the light to your brain.

Available Light

• Photographers generally use the light of the outdoors or what is called the available light.

• This is day light produced by the sun. • Daylight changes with the moods of the earth

(weather) and the time of day. • Sometimes light is filtered by clouds (diffused)

or directly hitting the earth. Some light reflects off of things and some light is absorbed (transmit) into things

Ways of Thinking About Light

• You have probably heard two different ways of talking about light:

• There is the "particle" theory, expressed in part by the word photon.

• There is the "wave" theory, expressed by the term light wave.

Light and the Ancients

• From the time of the ancient Greeks, people have thought of light as a stream of tiny particles. After all, light travels in straight lines and bounces off a mirror much like a ball bouncing off a wall. No one had actually seen particles of light, but even now it's easy to explain why that might be. The particles could be too small, or moving too fast, to be seen, or perhaps our eyes see right through them.

Light wave Theory

• The idea of the light wave came from Christian Huygens, who proposed in the late 1600s that light acted like a wave instead of a stream of particles.

• In 1807, Thomas Young backed up Huygens' theory by showing that when light passes through a very narrow opening, it can spread out, and interfere with light passing through another opening. Young shined a light through a very narrow slit. What he saw was a bright bar of light that corresponded to the slit. But that was not all he saw. Young also perceived additional light, not as bright, in the areas around the bar. If light were a stream of particles, this additional light would not have been there. This experiment suggested that light spread out like a wave. In fact, a beam of light radiates outward at all times.

Photon Theory• Albert Einstein advanced the theory of light further in

1905. Einstein considered the photoelectric effect, in which ultraviolet light hits a surface and causes electrons to be emitted from the surface. Einstein's explanation for this was that light was made up of a stream of energy packets called photons.

• Modern physicists believe that light can behave as both a particle and a wave, but they also recognize that either view is a simple explanation for something more complex. Most scientists and educators will talk about light as waves, because this provides the best explanation for most of the phenomena our eyes can see.

Light: Photons and Waves

• Isaac Newton discovered in 1672 that light could be split into many colors by a prism, and used this experimental concept to analyze light. The colors produced by light passing through a prism are arranged in a precise array or spectrum from red through orange, yellow, green, blue, indigo and into violet. The students' memory trick is to recall the name "Roy G. Biv" where each letter represents a color. The order of colors is constant, and each color has a unique signature identifying its location in the spectrum. The signature of color is the wavelength of light.

Prism of Light

Prisms can show us how light waves of energy from the sun are seen visually .Colors are frequencies and tell us what frequencies have the most and least energy.

“Roy G. Biv”

• Red• Orange• Yellow• Green• Blue• Indigo• Violet

Color Spectrum

Least Energy

MostEnergy

The spectrum of light most used in Photograph

R G B• RED

• GREEN• BLUE

Color Films are balance to these colors and your color monitors on computers are calibrated in RGB.

Color Temperature

• Color has a measurement scale with units called Kelvin's (k). A light bulb, the sun, candlelight etc… is described in warm or cool tones. Warm tones are seen as reddish and cool tones are seen as bluish.

• The measurement scale for color is the opposite of what we are used to. Instead of the higher number meaning hotter temperatures, the higher number refers to cooler colors (blues) and the lowest numbers are the reds or warmer colors.

Warmer Color

Kelvin Scale

1800K Candlelight

2500 Standard Light Bulb

5000K Daylight

7500K Shade

Cooler Color

BW vs. Color

• Black and white film• Doesn’t see color• It does record the energy

of waves of light – the brightest to dullest tones or “intensity of light.”

• Intensity referres to how strong the light of a light source.

• Digital Color/color film• Filters the color spectrum

into RED’s Greens and Blues and all the mixtures of those colors.

• Daylight tends to cast blue tones

• Sunset gold tones tone• It can record visual color

frequencies

Frequency of light= Color• Light waves also come in many frequencies. The frequency

is the number of waves that pass a point in space during any time interval, usually one second. It is measured in units of cycles (waves) per second, or Hertz (Hz).

• The frequency of visible light is referred to as color, and ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as violet. Again, the full range of frequencies extends beyond the visible spectrum, from less than one billion Hz, as in radio waves, to greater than 3 billion billion Hz, as in gamma rays.

Light Waves= Energy• As noted above, light waves are waves of

energy. The amount of energy in a light wave is proportionally related to its frequency (color): High frequency light has high energy; low frequency light has low energy. Thus gamma rays have the most energy, and radio waves have the least. Of visible light, violet has the most energy and red the least.

Low Frequency

light waves come in a continuous variety of sizes, frequencies and energies

High Frequency

So light waves come in a continuous variety of sizes, frequencies and energies. We refer to this continuum as the electromagnetic spectrum (Figure 2). Figure 2 is not drawn to scale, in that visible light occupies only one-thousandth of a percent of the spectrum

So light waves come in a continuous variety of sizes, frequencies and energies. We refer to this continuum as the electromagnetic spectrum (Figure 2). Figure 2 is not drawn to scale, in that visible light occupies only one-thousandth of a percent of the spectrum.

electromagnetic spectrum (Figure 2).

Light and the film plane

Images on your film or digital storage devices are really upside down when they are recorded. This is because the lens on your camera converge light rays through a hole and they reflect in the opposite direction that your eye sees them.

Cameras, in brief

In a pinhole camera, the hole is so small that light hitting any particular pointon the film plane must have come from a particular direction outside the camera

In a camera with a lens, the same applies: that a point on the film planemore-or-less corresponds to a direction outside the camera. Lenses havethe important advantage of collecting more light than the pinhole admits

pinholeimage atfilm plane

object

image atfilm plane

object

lens

Speeds of Light

• Light not only vibrates at different frequencies, it also travels at different speeds. Light waves move through a vacuum at their maximum speed, 300,000 kilometers per second or 186,000 miles per second, which makes light the fastest phenomenon in the universe.

• Light waves slow down when they travel inside substances, such as air, water, glass or a diamond. The way different substances affect the speed at which light travels is key to understanding the bending of light, or refraction, which we will discuss later.

When Light Hits an Object• When a light wave hits an object, what happens to it

depends on the energy of the light wave, the natural frequency at which electrons vibrate in the material and the strength with which the atoms in the material hold on to their electrons. Based on these three factors, four different things can happen when light hits an object: The waves can be reflected or scattered off the object.

• The waves can be absorbed by the object. • The waves can be refracted through the object. • The waves can pass through the object with no effect. • And more than one of these possibilities can happen at

once.

Most materials are transparent to some frequencies, but not to others. For example, high frequency light, such as gamma rays and X-rays, will pass through ordinary glass, but lower frequency ultraviolet and infrared light will not.

Transmission

Direct vs Diffused Light

• Direct• Light travels to earth in

a single plane• It is not obstructed by

clouds of filtration

• Diffused• Light is scattered by

clouds, trees, overhangs or a filter – This produces softer light

Types of Light other than Daylight• Laser light• Tungsten Light• Incandescent Light (Light bulbs)• Florescent Light• Holagen• LCD

Can you think of any other types of artificial light ?

In Class Assignment --

• Using your study notes, work with the person sitting next to you on the “Principle of Light” work sheet. Wait for teacher’s instructions.