Optics and light

●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 speed 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.