Light is a form of electromagnetic
radiation
in the range of 380 to 760 nm (0.000000001 meters) that stimulates the
retina
of the eye. Thus the phenomenon of seeing light depends on both the electromagnetic
radiation
and the response of the human eye.
Light travels in waves at a speed of 186,000 miles (about 300,000 kilometers) per second, and has the ability to bend around a sharp corner.
Light
can be considered either as a corpuscular flow or as a wave phenomenon.
The relative sensevity of the human eye at different wavelengths.
A graphic representation of an electromagnetic wave.
Support for the theory that light travels in waves came with the discovery of polarization, which indicated that the undulations of a light wave were transverse to the direction of propagation. Just as sound waves travel through air, light waves can travel through a vacuum.
The theory of a corpuscular flow is based on the assumption that light travels in packets of energy called quanta. The corpuscular unit is the photon, which is the radiant power released by a displaced electron. The light consists of an array of light waves arranged by order of magnitude of wavelengths. Part of the
spectrum
consists of visible wavelengths, with invisible wavelengths (infrared and ultraviolet) at either end.
Fig – 1: The light is polarized by a polarizing sheet, enable only half of the cycle to pass. Fig – 2: unpolarized light is not transmited by crossing polarizing sheets.
Light is often described in terms of rays in straight lines. If an object blocks the path of the rays, they will be reflected or absorbed, and will not be able to bend around an object. This creates an unlit area called a shadow. When a ray of light passes from one medium to another (for example, from air to glass) its direction changes. This phenomenon is called refraction. Yet another phenomenon, diffraction, is the manner in which light waves spread as they move through a barrier or a gap, resulting in
interference
patterns so that the original even field becomes a
pattern
of alternating light and dark.
Two water drops create patterns of circular ripples, analogous to electromagnetic waves.
Artificial light is produced by applying
electricity
to heat various materials.
Light
sources that produce light due to resistance of the filament to the electric current are called incandescent lamps. Discharge lamps produce light when the element that they contain, either a gas or a mineral, is excited by an electric spark.
Each type of
light source
has a distinctive color.
White
light, as perceived by the eye, is a combination of visible wavelengths in the spectrum. What we perceive as
white light
can also be created by mixing wavelengths of the three
primary colors
such as blue, red, and green, or two
complementary colors
such as blue and yellow.
In order to create a
beam
of colored light in the theatre, color filters are used which subtract certain wavelengths from the
spectrum
that comprises white light, creating a partial spectrum.
