what is light?. light visible light is a form of energy that can be detected by cells in our eyes....
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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
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