1. Sources of Light 1.Sun -the most abundant natural source of light on Earth -produced through nuclear fusion where hydrogen (H) combines to form helium (He)

2. Sources of Light 2.Incandescence -light emitted by the high temperature of a solid material (tungsten filament) when electricity goes through it e.g. lightbulb -inefficient (only convert 5% of electrical energy into light and remaining 95% lost as heat)

3. Sources of Light 3.Electrical Discharge -light emitted from a heated gas that has an electric current passing through it e.g. streetlights, lightning

4. Sources of Light 4.Fluorescence -electricity run through the bulb releases ultraviolet light which is converted into visible light Positives: 1) 20% efficiency 2) longer life Negatives: 1)possess hazardous material (mercury) 2) more expensive 3) uncomfortable light

5. Sources of Light 5.Phosphorescence -light emitted due to exposure of the source to ultraviolet light -glows even after that source is removed e.g. nightglow frisbee

6. Sources of Light 6.Chemiluminescence -light produced by a chemical reaction without a rise in temperature e.g. glowsticks

7. Sources of Light 7.Bioluminescence -light produced in the cells of a living organism e.g. fireflies, jellyfish

8. Sources of Light 8.Triboluminescence -light produced by the friction of scratching or crushing certain crystals e.g. quartz

9. Sources of Light 9.Light-Emitting Diode (LED) -light produced as a result of an electric current flowing through a semiconductor e.g. tree lights