Basic Photography Course

CHARACTERISTICS OF LIGHT

The subject of light as a form of radiant energy has

been theorized upon, experimented with, and studied by
many physicists and scientists. Until about three
centuries ago, no one had developed a reasonable theory
of the nature of light. Then Max Planck, a physicist,
published a theory in which light was supposed to
consist of a stream of high-speed particles. Planck
theorized that any light source sent out an untold number
of these particles. This then was the quantum theory.
The quantum of light is called the photon. The quantum
theory is used to explain X ray, radiation, and
photoelectricity.

WAVELENGTH, SPEED, AND FREQUENCY

About the same time other physicists, Christiann

Huygens and Thomas Young, introduced a theory called
the wave motion theory. The wave motion theory is used

to explain reflection, refraction, diffraction, and
polarization. In wave motion theory, light, wavelength,
speed, and frequency are important characteristics, and
they are interrelated.

The wavelengths of light are so small that they are

measured in nanometers (nm). A nanometer is equal to
one millionth of a millimeter. Wavelengths of light range
from about 400nm to 700nm in length and travel in a
straight-line path.

The speed of light varies in different mediums. In

air, light travels about 186,000 miles per second. In a
denser medium, such as glass, light travels even more
slowly. Furthermore, in a denser medium, the speed is

different for each color of light. Wavelength is the
distance from the crest of one wave to the crest of the

next wave (fig. 1-2). Frequency is the number of waves
passing a given point in

1 second. The product of the

two is the speed of light.

Therefore:

Speed = Wavelength

frequency, or

Wavelength =

Speed

Frequency

Since the speed of light in glass is slower than in air,

the wavelength must also be shorter (fig. 1-3). Only the
wavelength changes; the frequency remains constant.
Hence we identify a particular type of radiation (color
of light) by its wavelength, bearing in mind that we are
speaking of the wavelength in air.

EMISSION OF LIGHT

To the photographer, there are two important

characteristics of the way light travels. First, in a given
medium, light always travels in a straight line. Second,
in a given medium, it travels at a constant speed.

Figure 1-3.Variation in speed and wavelength.

1-2

contents

Basic Photography Course

<- previous page

next page ->


DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> Figure 1-2.Wavelength. CHARACTERISTICS OF LIGHT The subject of light as a form of radiant energy has been theorized upon, experimented with, and studied by many physicists and scientists. Until about three centuries ago, no one had developed a reasonable theory of the nature of light. Then Max Planck, a physicist, published a theory in which light was supposed to consist of a stream of high-speed particles. Planck theorized that any light source sent out an untold number of these particles. This then was the quantum theory. The quantum of light is called the photon. The quantum theory is used to explain X ray, radiation, and photoelectricity. WAVELENGTH, SPEED, AND FREQUENCY About the same time other physicists, Christiann Huygens and Thomas Young, introduced a theory called the wave motion theory. The wave motion theory is used to explain reflection, refraction, diffraction, and polarization. In wave motion theory, light, wavelength, speed, and frequency are important characteristics, and they are interrelated. The wavelengths of light are so small that they are measured in nanometers (nm). A nanometer is equal to one millionth of a millimeter. Wavelengths of light range from about 400nm to 700nm in length and travel in a straight-line path. The speed of light varies in different mediums. In air, light travels about 186,000 miles per second. In a denser medium, such as glass, light travels even more slowly. Furthermore, in a denser medium, the speed is different for each color of light. Wavelength is the distance from the crest of one wave to the crest of the next wave (fig. 1-2). Frequency is the number of waves passing a given point in 1 second. The product of the two is the speed of light. Therefore: Speed = Wavelength x frequency, or Wavelength = Speed Frequency Since the speed of light in glass is slower than in air, the wavelength must also be shorter (fig. 1-3). Only the wavelength changes; the frequency remains constant. Hence we identify a particular type of radiation (color of light) by its wavelength, bearing in mind that we are speaking of the wavelength in air. EMISSION OF LIGHT To the photographer, there are two important characteristics of the way light travels. First, in a given medium, light always travels in a straight line. Second, in a given medium, it travels at a constant speed. Figure 1-3.Variation in speed and wavelength. 1-2 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
	WWW.DOFMASTER.COM © 2006 Don Fleming. All rights reserved.