1. Sources of Light

2. How is light produced? Luminous objects, produce their own light
E.g. the sun
Non-luminous objects, do not produce their own light
E.g. the moon
Most objects are non-luminous

3. Sources of Light 1. Incandescence
The production of light from high heat
E.g. an incandescent bulb or a candle

4. 2. Electric Discharge Electric current passing through a gas.
E.g. a street lamp or neon sign

5. 3. Phosphorescence
Absorption of UV radiation followed by the emission of visible light over an extended period of time.
E.g. glow-in-the-dark toys

6. 4. Fluorescence The immediate emission of visible light
E.g. fluorescent bulbs (tube or compact)

7. 5. Fluorescence continued…
The bulb is filled with mercury gas and coated with a phosphor
Electricity causes the mercury atoms to emit UV radiation, which are absorbed by the phosphor and released immediately.

8. 6. Chemiluminescence Chemical reaction creates light No heat produced
E.g. glowstick

9. 7. Bioluminescence Living organisms performing chemiluminescence
E.g. fireflies, angler fish
Angler fish

10. 8. Triboluminescence
Scratching, crushing, or rubbing certain crystals creates light (friction)
E.g. rubbing two sugar cubes together or biting Wint-O-Green lifesavers

11. 9. LED’s (light emitting diodes)
An electric current flowing through a semiconductor
Very energy efficient
E.g. Christmas lights, some TV’s