A Few Facts About Light

Light is not an easy concept to define and fully understanding it continues to be a challenge
for modern physics.  Light is energy in the form of very small, mass-less particles called
photons.  Photons travel in a wave-like pattern at the speed of light (186,000 miles per
second).  Even though all photons travel at exactly the same speed, not all of them have the
same wavelength or frequency.  Just as a waves traveling through water have a wavelength
(the distance between wave crests) and a frequency (the number of wave crests passing a
certain point in a designated unit of time), light has a wavelength and a frequency.  

Scientists talk about a hypothetical “spectrum” of light that contains all of the possible
frequencies and wavelengths- the electromagnetic spectrum.  This spectrum includes:
gamma rays, x-rays, ultraviolet light, visible light, microwaves and radio waves (these are
listed in terms of increasing frequency and decreasing wavelength).  As you go down the
electromagnetic spectrum different forms of light have different qualities and they are able
to affect matter in vastly different ways.

The higher the frequency of a light ray, the more energetic it is.  This is why only very hot
objects, or high velocity particles can generate substantial amounts of gamma rays or x-
rays.  Some forms of electromagnetic radiation can warm us or burn us, some can cause
mistakes in our DNA molecules on contact with them and other forms of radiation harmlessly
pass right through us.  But there is only one portion of the spectrum that is perceptible to
our eyes- the visible portion.  The colors that we can see are actually different frequencies
of light.  Red light has the longest wavelength and the lowest frequency and purple light has
the shortest wavelength and the highest frequency.  The three types of cellular receptors in
our eyes each pick out a different portion of the visible spectrum- there is one type for red,
one for green and one for blue.  In fact, all of the colors that we perceive are simply different
combinations of these three portions of the visible spectrum.  

Light can be 1) reflected by a mirror, 2) it can be bent (refracted) when it passes between
mediums of different densities (it can also be bent by gravity) and, 3) it can be diffracted
(made more or less prominent) by the interference of other light waves.  

Light necessitates no medium, save that of physical space, to propagate. However, light can
travel through many types of mediums like some liquids and gasses. Because photons can
be blocked or absorbed by atoms though, light is usually diminished or retarded as it
passes through a material medium like water or air.  On the other hand in a perfect vacuum-
without any intervening massive particles- light travels at its fastest and maintains its energy
indefinitely.

Light can be created by heating up matter so hot that it glows.  An incandescent light bulb is
a great example of this.  The tungsten wire in a light bulb is so thin, that it creates a
substantial amount of resistance for the electric current running through it.  This electrical
resistance is transformed into two things- heat and light.  

But how is the light created?  Light is actually emitted from individual atoms.  When an atom
takes up energy from its environment it can store it in its electrons.  The electrons actually
expand their (discrete) energy levels or “orbitals” as the atom absorbs energy.  Thus
energy can saved by an atom’s electrons as potential energy.  When the electrons move
back down from their more energetic orbitals, to the less energetic ones, the potential
energy is released as a photon of light.