Light Sources

As we said before, light is a form of energy; to create light, another form of energy must be supplied. There are two basic types of light sources: Incandescence and Luminescence. Incandescence involves the vibration of entire atoms, and luminescence involves only the electrons.

Incandescent Light:

Incandescence is light from heat energy. If we heat something to a high enough temperature, it will begin to glow. Incandescent light is produced when atoms are heated and release some of their thermal vibration as electromagnetic radiation. This is the most common type of light that we see everyday, like sunlight, regular light bulbs -not florescent- and fires. Light is produced by incandescence when light comes from a heated solid.

Incandescent light is also known as "black body radiation". This name arises from the studies of this type of light by scientists. They modeled their theories on ideal materials that would absorb all colors of light, appearing to be "black bodies". Depending on how hot the material is, the photons released have different energies and different colors. At lower temperatures, these materials emit radiation in the infrared wavelengths, which we feel as heat. For example, most of the energy emitted by a fire is infrared. When the temperatures increase, these materials would glow red, then orange, then yellow and eventually "white hot. Ideal black body materials do not exist, however, most substances are closed enough that this color sequence can be observed. Let's take a look at the following types of incandescent light:

The Sun:

The Sun is the central member of the solar system. It governs the motions of the other members in the orbit because of its gravitational force. The Sun provides almost all of the heat and all of the light and other forms of energy that are necessary for life on our planet. Although the sun is a rather ordinary star, it is very important to the inhabitants of the Earth; it is the source of all of the Earth's energy. The Sun and the Stars glow by incandescence.

Light Bulbs and Fires:

Fire and light bulbs provide light by the same process, incandescence.

In fires, chemical reactions release heat, releasing gases and raising materials to high temperatures, where the materials and the gases incandescence. Different temperatures are produced and result in different colors.

Light bulbs use electricity to produce the heat. Inside a light bulb, electrical current runs through a thin wire and heats the wire to a high temperature, causing the wire to incandesce. The brighter and the whiter temperature, the higher the temperature must be. In incandescent lamps, the filament of the light bulb is made of tungsten, a special metal which can stay at a high temperature for a hundred hours without burning.

To determine the amount of energy a light bulb uses, we can use the following rule: one watt is equal to one joule of energy per second, so a 60 watt light bulb uses 60 joules per second and 216,000 joules per hour.

Luminescent Light:

Luminescence is "cold light", it is light from other sources of energy, which can take place at normal and lower temperatures. Luminescent light occurs at lower temperatures than incandescent light. It is produced when an electron releases some of its energy to electromagnetic radiation. Electrons need to have energy at specific energy levels, when an electron jumps down to a lower energy level, it releases a specific amount of energy which becomes a photon, or light of a specific color. To have continuous luminescence, it is required to have something to continuously give the electrons a boost to a higher energy level in order to keep the cycle going. This boost may be provided by different sources as: electrical current, as in florescent lights, neon light, mercury-vapor street lights, light emitting diodes, television screens and computer monitors, animals like fire-flies, etc.

There are several varieties of luminescence, each of those types is named according to what the source of energy is, or what the trigger for the luminescence is. Let's take a look at the following:

Florescent Lights and TV:

Three of the most common applications of luminescence are in computer monitors, televisions, and florescent lights. Television and florescent lights rely on phosphors -special chemicals that release light when excited by electricity, radiation and other methods. Florescent lights employ two types of luminescence, electro luminescence and photoluminescence.

Neon Lights:

Neon lights produce their light through electro luminescence, which is high voltage that forces current through the gas that excites it and causes it to emit light. Here is a list with common colors and the gases associated with them:

To obtain red- orange, we would use neon
To obtain blue, we would use mercury
To obtain green, we would use mercury vapor
To obtain gold, we would use helium in amber tube
To obtain yellow, we would use sodium.


Bioluminescence is defined as the generation of light by living organisms, like deep-sea species of squids, octopus, worms, and mollusks and the firefly in the air.

Deep-sea Life: The light from deep-sea life is produced by bacteria or special cells that live within the fish.

Firefly: The light that a firefly produces is defined as "cold" because it is very efficient and little of it is converted to heat. The light organs of the firefly are located on the underside of the abdominal segments. They are richly supplied with nerves and "trachae" which supplies the oxygen necessary for light production.