(10.1) Sources of Light

Sources of Light Luminous Source Non-Luminous Source: produces its own light eg. the sun, a light bulb, a camp fire, a firefly Non-Luminous Source: does not produce its own light. eg. the moon, a person, a pencil

Types of Light Incandescence Electric Discharge Phosphorescence Fluorescence Chemiluminescence Bioluminescence

Light from Incandescence the production of light as a result of high temperature produced by a light bulb, a candle, molten metal.

How does a Light Bulb Work? electricity passes through a thin wire filament which gets so hot that it gives off visible light and infrared light. bulbs contain non-reactive gases so that the filament can’t react with oxygen. very inefficient source of light because only 5%-10% of the electricity is converted to visible light. up to 95% of the electric energy is wasted on the production of heat (infrared radiation). Video: How a lightbulb works

Electric Discharge the production of light by passing an electric current through a gas. different gases produce different colors of light (e.g., Neon gas produces red light). lightning is a form of electric discharge through the air of Earth’s atmosphere. Video: Neon Lights

Light from Fluorescence fluorescence occurs when an object absorbs ultraviolet light and immediately releases the energy as visible light.

How do Fluorescent Light Bulbs Work? tube is filled with mercury vapour electricity causes vapour to emit ultraviolet light. ultraviolet light strikes fluorescent material in inner surface of glass and causes visible light

Fluorescent Lights Video: How Fluorescent Lights work

Compact Fluorescent Bulbs since much less energy is lost as heat, fluorescent bulbs are about 5 times more efficient than incandescent bulbs Because they contain small amounts of mercury vapour, care must be taken when disposing of compact fluorescent bulbs

Light from Phosphorescence some materials absorb ultraviolet energy and hold onto it while slowly releasing visible light over a period of time glow-in-the-dark objects

Light from Chemiluminescence production of light as a result of a chemical reaction with little or no heat production used in situations when it is unsafe to use electricity ie. underwater divers Video: Glowsticks

Light from Bioluminesence production of light in living organisms as a result of a chemical reaction with little or no heat production Video: Glow Worms Video: Fish

Homework Read pg. 403-410 Do #3 – 5, 8 on pg. 410