only because they reflect the light that
from some luminous source.
reaches them
When light strikes a medium and is neither reflected
nor transmitted (passed on), it is said to be absorbed.
Black cloth or areas of dark forest, for instance, absorb
more light than objects such as a white sheet or a coral
sand beach. When light comes in contact with the
surface of an object, a certain degree of reflection, and
some absorption, always takes place.
A medium that does not allow light to pass through
it is opaque. An opaque material may also reflect light.
When an object is opaque and the light is not reflected,
it is absorbed by the object. When light is absorbed, its
energy is converted and it no longer exists as light.
The color of an object is determined by the way it
absorbs light falling upon it (incident light). A woman's
dress appears red when it absorbs the blue and green rays
of white light and reflects the red waves. A lawn appears
green because the grass blades absorb the red and blue
rays of light and reflect the green rays.
Neutral colors, such as white, black, and the various
tones or values of gray, actually absorb almost equal
proportions of the colors of light. Varying reflective
powers account for their differences. White is highly
reflective, while an object of absolute blackness, no
matter how much light falls on it, can never be recorded
on film except by contrast.
In addition to being reflected and absorbed, light
rays may be transmitted. They may also pass through
some medium they encounter. When objects can be
clearly seen through the medium, the medium is
transparent. A transparent medium transmits light rays
in a regular, or uniform, pattern. When the medium
transmits light but breaks up the orderliness of the
pattern, sending the transmitted rays in many directions,
the medium is translucent. In other words, a medium is
said to be translucent when light is visible through it, but
objects are NOT clearly distinguishable. Thin fabrics
and frosted glass are examples of translucent materials
that allow the passage of diffused light (fig. 1-7). One
important form of transmission is termed refraction.
The change of direction that occurs when a ray of
light passes from one transparent substance into another
substance of different density is called refraction.
Refraction enables a lens to form an image. Without
refraction, light waves behave as X rays and pass in
straight lines through all suitable substances without any
control of direction, and only shadow patterns can be
made with them. Refraction occurs because light travels
at different speeds in different transparent substances.
The speed of light in each transparent substance is called

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