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Visible Light
There are many wavelengths of light. The different wavelengths of light have different colors and
different energies. Light of different energies interacts with objects differently.
White Light
White light, such as the light produced by the Sun, is composed of different wavelengths of light.
Each wavelength of light is a different color. The components of white light can see be observed by
using a prism to bend, or refract the light and separate them according to wavelength.
Image courtesy of NASA
When white light enters a prism, the different colors of light refract different amounts. When the light
exits the prism, it is seen as all the different colors of the rainbow positioned side by side.
Interaction of Light with Materials
Each wavelength of light has a different characteristic energy. Objects or materials of different color
or composition may be able to take in, or absorb, some of these energies but not others.
When light strikes an object, the object can absorb, reflect, refract, or transmit the light. An object that
absorbs or reflects only a portion of the light striking it is translucent. An object that absorbs or reflects
all the light striking it is opaque. Colorless transparent objects let nearly all of the light pass through.
Absorption & Heat
Absorption is the opposite of reflection. Absorption occurs when an object takes in a wave's energy.
As the wave transfers energy to the object, the object's energy increases, and therefore its
temperature also increases. Light and other electromagnetic waves can warm objects in this way.
The amount that the temperature of the object increases depends on several factors:
•
the amount of time that the light shines on the objects
•
the intensity of the light striking the object
•
the percentage of light that is absorbed
For example, the umbrella in the photo below is blocking light waves above a small area of sand.
That sand is not absorbing as much light energy as the surrounding sand, so its temperature is not
increasing as much.
The sand in the umbrella's shadow is cooler than the surrounding sand.
The third factor listed above—the percentage of light that is absorbed—varies with an object's
properties. One property that has a significant influence on how much light is absorbed is an object's
color. Dark colors cause an object to absorb more light and also cause the object to heat up more.
Since black objects absorb more light, they get hotter faster than other objects when they are left in
the sunlight.
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