SOURCES LIGHT

1) Natural Sources of Light

SUN!

•most important natural source of light

Other Stars

Lightning

Fires

Bioluminescence

• the production of light as a result of a chemical reaction in a living thing

• sea creatures use this in very deep water where no light is

• use light to see prey/scare predators/camouflage

angler fish

• long spine with a bulb• used as a lure to attract prey

Jellyfish• use light to attract fish into their

tentacles

Flashlight fish

• use light to help to keep in a school

Fireflies

• use to attract mates

2) Artificial Sources of Light

Incandescent Light• Production of light as a result of high

temperature• bulbs contain a filament or thin wire

(tungsten) that is heated up by electricity and then glows

• Only 5%-10% effective

Electric Discharge

• Production of light by passing an electric current through a gas

• E.g. halogen gases used often (e.g. neon)

Fluorescent Light

• the immediate emission of visible light as a result of the absorption of UV light

• E.g. detergents, highlighters, fluorescent lights

• Demo: rocks + UV light

• bulb filled with a gas such as mercury vapour

• When mercury vapour is exposed to electricity it emits UV light

• bulb is coated with a white powder called phosphor

• phosphor glows if exposed to UV radiation

Compact Fluorescent Bulbs• even though compact fluorescent

lights are more efficient than incandescent light bulbs, still 80% of energy is converted into heat

Phosphorescent Light• The process of

producing light by the absorption of UV light resulting in the emission of visible light over an extended period of time

• Different from fluorescent because phosphorescent materials glow in the dark for some time after being energized by light

Chemiluminescence• light produced from chemical reactions

(little heat produced)• ex. luminol used in forensics: glows when

it reacts to iron in blood • ex. glow sticks

How Glow Sticks Work

Triboluminescence

• Production of light from friction• rubbing crystals together• quartz used in rattles by Aboriginal

people for flash lights

• Complete Worksheet before end of class.

• Do pg. 476 #1-4, 6,9,10• You should have this mostly

done by the end of class.