1. (10.1) Sources of Light

2. 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

3. Types of Light Incandescence Electric Discharge Phosphorescence
Fluorescence
Chemiluminescence
Bioluminescence

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

5. 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

6. 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

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

8. 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

9. Fluorescent Lights
Video: How Fluorescent Lights work

10. 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

11. 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

12. 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

13. 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

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