Types of Light
To understand
light you have to know that what we call light is what is visible to us. Visible light is the light that humans can see. Other animals can see different
types of light. Dogs can see only shades of gray and some insects can see light
from the ultraviolet part of the spectrum. The key thing to remember is that
our light is what scientists call visible light.
Scientists also call light electromagnetic radiation. Visible light is only one small portion of a
family of waves called electromagnetic (EM) radiation. The entire spectrum of these EM waves
includes radio waves, which
have very long wavelengths and both gamma rays and cosmic
rays, which are at the other end of the spectrum and have very small
wavelengths. Visible light is near the middle of the spectrum.
It's all Energy
The key thing
to remember is that light and EM radiation carry energy. The quantum theory suggests that
light consists of very small bundles of energy/particles; it's just that
simple. Scientists call those small particles photons, and the wavelength
determines the energy and type of EM radiation, and the number of photons tells
you how much radiation there is. A lot of photons give a brighter, more intense
type of light. Fewer photons give a very dim and less intense light. When you
use the dimmer switch on the wall, you are decreasing the number of photons
sent from the light bulb. The type of light is the same while the amount has
changed.
Different Speeds of
Light?
As far as we know, all types of light move at
one speed when in a vacuum. The speed of light in a vacuum is 299,792,458
meters per second. That speed is really fast, but even when you're traveling
that fast, it takes a while to get places in space. It takes about seven minutes
for light from the Sun to reach Earth. It takes over four years for the light
from our Sun to get to the nearest star. It would take a particle of light over
100,000 years to get from one side of our galaxy to the other side. All of
those values are light moving through a vacuum. You can slow light down in
other substances such as the atmosphere, water, or a diamond. Light moves at
about 124,000,000 meters per second (less than half the speed in a vacuum) in a
diamond.
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