1. Technology that Produces Light 1. Incandescence – when objects are heated enough, they glow. Ex. Incandescent Light Bulbs – electricity heats up metal filament – electricity heats up metal filament – convert only 5% of energy into light! – convert only 5% of energy into light!

2. 2. Fluorescence – chemicals absorb UV energy and change it into light. Different chemicals make different colours. Fluorescent Light Bulbs – electricity excites mercury and argon gas, which then makes white powdered coating glow. These are 20% efficient! Phosphors – Chemicals that creates glow in the dark paint.

3. Discharge lamps – electricity excites noble gases, which then make different coloured phosphors in a pixel glow. (neon lights, plasma TV) * LCD displays work differently - electricity excites bands of chemicals which cause them to turn and let light from a fluorescent bulb pass through a coloured filter (Monitors, clocks, TV).

4. 3. Light Emitting Diode (LED) – electricity flows through a semiconductor which then releases light. Very efficient but expensive (back lights).

5. 4. Chemoluminescence – light produced by a chemical reactions ex. glow sticks **Some animals can do this inside their bodies (called bioluminescence) Video Video2

6. How would your life change if we didn’t have technology to make light? Pg. 433 #1 – 3