The Production of Light Shedding some light on the world…

How We See We see by light entering our eyes This happens in 1 of 2 ways: Luminous objects create their own light Light bulb, Sun, TV Non-Luminous objects only reflect light Paper, planets, desks

How Light is Produced Luminous Objects produce their own light in a variety of ways. For example: Incandescence Electric Discharge Phosphorescence Fluorescence Chemiluminescence Bioluminescence Triboluminescence Light-Emmiting Diode (LED) LASER

Incandescence Producing light from a glowing hot object Colours produced depend on the temperature As temperatures increase, colours change from red, to yellow, to white, to a blueish-white. Examples: Stove, fire, incandescent light bulb

Electric Discharge Producing light by passing electric current through a gas Electrons are excited to higher orbits and then emit light when they fall back down Different gasses produce different colours Examples: Lightening, neon lights

Phosphorescence Producing light by absorbing UV light and emitting visible light over time Phosphors store the energy until later Examples: Glow in the dark stickers, some watches

Fluorescence Producing light by absorbing UV light and emitting visible light immediately Examples: Fluorescent lights, “black lights”, highlighters

Fluorescent Lights Makes use of electric discharge and fluorescence Electric discharge in the tube causes mercury in the tube to emit UV light Fluorescent materials on the outer wall of the tube then glow in the visible range They don’t emit true white light, just a few distinct colours

Chemiluminescence Production of light as the result of a chemical reaction Little to no heat is produced No electric current required Examples: Glow sticks

Bioluminescence Chemiluminescence occurring in a living organism Developed for various reasons Examples: Firefly, Glow worm, Anglerfish

Triboluminescence Production of light from friction Certain crystals produce light when crushed, rubbed or scratched No known practical applications Examples: Eating wintergreens hard candy

Light-Emitting Diode (LED) Producing light by passing electricity through a semi-conductor Semi-conductor: A material allowing electricity to pass in one direction only Low heat produced and very energy efficient Examples: Glowing light on electronics, Christmas lights, traffic lights

LASER Light Amplification by Stimulated Emission of Radiation Produced using either special gasses or crystals Laser light is all one colour (wavelength) traveling in a very narrow, focused beam High and low energy lasers are available