What is light?What is light?

Light Light Visible light is a form of energy that can be Visible light is a form of energy that can be

detected by cells in our eyes.detected by cells in our eyes. Light is an electromagnetic wave.Light is an electromagnetic wave.

LightLight

Electromagnetic waves are a form of Electromagnetic waves are a form of energy that travel as far as a wave at energy that travel as far as a wave at the speed of light (3.0 x 10 8m/s) the speed of light (3.0 x 10 8m/s) and do not need a medium to travel and do not need a medium to travel in (ie. They can go through space.in (ie. They can go through space.

Electromagnetic Spectrum Electromagnetic Spectrum

Production of LightProduction of Light

Luminous Luminous produces its own light.produces its own light.

Non-luminous Non-luminous Only reflects light. We see things by Only reflects light. We see things by

detecting this reflected light.detecting this reflected light.

Incandescent lightIncandescent light

Old fashioned light bulbsOld fashioned light bulbs Filament heated to point of Filament heated to point of

incandescence (gives off white light)incandescence (gives off white light) 95% of energy lost as heat,95% of energy lost as heat,

5% = light5% = light

Production of LightProduction of Light

Electric discharge: Electric discharge: produced when an produced when an electric current electric current passes through a passes through a gasgas

Ex. Neon lightsEx. Neon lights

PhosphorescencePhosphorescence

Substances which Substances which absorb energy absorb energy (usually UV) and (usually UV) and release it back as release it back as light over a long light over a long period of time.period of time.

Example: glow-in-Example: glow-in-the-darkthe-dark

Fluorescence Fluorescence

Substances which Substances which absorb energy (usually absorb energy (usually UV) and immediately UV) and immediately releases it back as light.releases it back as light.

Black light cause Black light cause certain substances to certain substances to fluorescefluoresce

Detergent contains Detergent contains substances that substances that fluoresce to make white fluoresce to make white shirts look brighter.shirts look brighter.

Fluorescent lightFluorescent light

Fluorescent light Fluorescent light Electricity excites Electricity excites

mercury vapour in the mercury vapour in the tube so it emits UVtube so it emits UV

UV strikes phosphorous UV strikes phosphorous powder that coats the powder that coats the tube. The powder tube. The powder fluoresces fluoresces

Very little heat is Very little heat is produced. 4-5x more produced. 4-5x more efficient than efficient than incandescentincandescent

ChemiluminescenceChemiluminescence

Light produced by Light produced by the chemical the chemical reaction between reaction between two chemicalstwo chemicals

Ex. Glow sticksEx. Glow sticks

Bioluminescence Bioluminescence

Light is produced when a living Light is produced when a living organism uses chemiluminesence.organism uses chemiluminesence.

Ex . Firefly, Glow wormsEx . Firefly, Glow worms

Light Emitting Diode (LED)Light Emitting Diode (LED)

Called a semi-Called a semi-conductor that conductor that glow when glow when electricity passes electricity passes through it (one way through it (one way only)only)

Very little heat is Very little heat is producedproduced

Not very brightNot very bright