# Difference between revisions of "Nature of light"

The beauty of a gemstone depends almost entirely upon the way it effects the light. The fire of a Diamond and the play of colors in an Opal are just two examples.

Scientists recognise two different theories to explain the way in which light is transmitted:

• The electromagnetic wave theory
• The quantum theory

Both theories are important to learn so you may understand the causes of color in gemstones.

## The electromagnetic wave theory

### Basic

This theory was developed by Dutch scientist Christian Huygens and later explored by others.

Light is a form of energy traveling in a wave motion.
It can be compared to what happens when you throw a brick in a puddle of water: the watersurface starts to vibrate and these vibrations cause circular waves.

[[Image:]] (which explains wavelength and amplitude)

The wave motions of light are not circular but spherical.
We can't see the light because:

• It travels too fast. The velocity of light (in air) is approx. 300,000 km/second.
• The individual waves are too small.

Note: although we can't see light we can see color. This is caused by absorption.

tansversal light

The light waves are transversal . This means that light travels in all directions in a straight line from its source.

There is a relationship between wavelength and color of light which is explained by what we call the electromagnetic spectrum. Which is explained below.

## The quantum theory

### Basic

This theory was developed by Einsten and Planck.

It states that lightenergy can be absopred and emitted only in small and discrete amounts, called "quanta" (later known as "photons"). This theory is used to explain certain causes of color in gemstones and the phenomenom of fluorescence.
Fluorescence is the emission of visible light by a substance, such as a gemstone, when irradiated by energy of a shorter wavelength. Some rubies can be made to glow like red-hot coals when they are bombarded by ultra-violet radiations.