1. 10.1 Sources and Nature of Light
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2. Light Emissions
For all light sources, atoms absorb some form of energy.
Excited atoms release energy, often in the form of light.
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3. Light from the Sun
H atoms fuse together to form He (fusion reactions).
Energy released from fusion excites gas atoms on outer layers.
Excited atoms emit light.
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4. Light from Incandescence
Incandescence = light emitted from material because of high temperature
Incandescent light bulbs have tungsten (W) wires.
95% of electrical energy released as heat.
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5. Light from Electric Discharge
Sodium vapour bulbs (some streetlights) have Na + a small amount of Hg vapour inside.
Electric current moves between electrodes at each end, exciting gas atoms.
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6. Fluorescence
Fluorescent bulbs are coated with phosphor & have Hg vapour inside.
Electric current excites Hg atoms, which emit UV light (not visible).
Phosphor absorbs UV & emits visible light (phosphorescence).
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7. Efficiency of Fluorescent Lights
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20% vs. 5%

8. Uses of Fluorescence
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9. Luminescence
Luminescence is light generated without heating an object, e.g., fluorescence.
Phosphorescence is light emitted due to exposure to UV light, that continues to be emitted.
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10. Chemiluminescence
Light generated by energy released in a chemical reaction.
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11. Bioluminescence
Light produced by living organisms due to chemical reactions in the living cells.
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12. The Nature of Light
Light energy travels in electromagnetic waves (involve electric & magnetic fields).
Wavelength = distance from one crest of a wave to the next
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13. Electromagnetic Spectrum
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