Where does light come from?

Heating metals If a metal is heated enough it will start to give off light. Why?

Light is produced by excited atoms Atoms are the basic particles from which everything is made. Sometimes atoms absorb energy from their surroundings and become “excited”. Under the right conditions this energy can be released from the atom as light. So, light is a form of energy released from excited atoms. How do we excite atoms?

Incandescence (Hot Light) When the metal was heated, the atoms absorbed heat energy and converted it to light. This process is called incandescence. Sources that produce light this way are called incandescent light sources HEAT ENERGY  LIGHT ENERGY

Incandescent Light Bulbs These are newer style lightbulbs that you may be more familiar with. The spiral bulb is a compact fluorescent lightbulb (CFL), and the second one is a light emitting diode (LED) bulb. More on those later.

Ban the incandescent! Many governments are encouraging people to switch from these older style bulbs to CFL or LED bulbs. Some countries, like Australia, have even taken steps to completely ban them. Do some quick online research and see if you can discover why this is?

Luminescence (cold light) Emission of light from a substance that does not result from heat. Remember… Step 1: Atoms absorb energy and become excited. With incandescence they absorb heat energy. With luminescence they absorb other types of energy. From chemical reactions From other types of light, e.g. ultra-violet light Step 2: The atoms excited atoms re-emit that energy as visible light.

Some Luminescent Light Sources Fluorescent sources Phosphorescent sources Chemiluminscent sources Bioluminescent Sources LED sources

Fluorescent Sources of Light Fluorescent Sources High energy, invisible UV light is absorbed by some particles, then re-emitted as visible light. This is called fluorescence.

Ultraviolet light energy  energy absorbed by particles  visible light energy Fluorescent Sources

Sources of Light Phosphorescent Sources These sources collect and hold light, reemitting it slowly over a period of time. This is called phosphorescence.(glow-in- the-dark)

Light energy  energy absorbed by particles  visible light energy (over time) Phosphorescent Sources

Similar to fluorescence except that phosphorescent sources release the energy over a long period of time. Fluorescent sources release their energy immediately.

Sources of Light Chemiluminescent Sources Some chemical reactions give off light. This is called chemiluminescence.

Chemical energy  visible light energy Chemiluminescent Sources

Sources of Light Bioluminescent Sources Some living creatures are able to produce light as a result of chemical processes in their bodies. This is called bioluminescence.

Chemical energy  visible light energy Bioluminescent Sources

Sources of Light LED Sources LED stands for Light-Emitting Diode. The light from LEDs results from the movement of electrons in the diode. Think of it as electrical energy converted directly into light energy.

Chemical energy  visible light energy Bioluminescence LED Sources