Sources of Light SNC2P – Optics

The Production of Light Objects that produce light are said to be luminous. Ex: star, burning candle, light bulb… Objects that we see because light passes through them or reflects (bounces off) from them are called non-luminous. Most objects are non-luminous. Ex: moon, stop sign, mirrors, clothing… Luminous objects give off light through a physical or chemical change. There are a number of ways this can happen:

Incandescence Light is given off when an object is heated. An object that gives off light when heated is said to be incandescent. How the heat is created depends on the situation or technology being used: Lava is a liquid rock (metal) that glows orange when heated by the Earth Sparks from a grinder are metal pieces that have been heated by friction The filament in a light bulb produces light when heated by electricity Burning wood produces light through a chemical change

Electric Discharge An electric current passing through a gas will sometimes produce light. Examples: Lightning Northern Lights Neon signs are tubes filled with gases like neon sodium, helium, and mercury. As electricity passes though the gas, a unique colour is produced.

Fluorescence Light is given off when a fluorescent substance is struck with electromagnetic energy. Examples: Fluorescent tubes are lined with a fluorescent powder and filled with a mercury vapour. As electricity passes through the mercury vapour, the mercury atoms release UV light. This UV energy hits the fluorescent powder, causing it to produce visible light. Road paint

Phosphorescence Substances that absorb energy and give off light long after the energy source has been removed are phosphorescent. Examples: Watch faces glow in the dark shirts

Chemiluminescence Light being produced from chemical reaction without the production of heat. Examples: Fireflies Breaking a glow stick causes two chemicals to mix. They react together and produce light.

Bioluminescence Organisms that produce light are bioluminescent Examples: Fireflies Angler fish deep in the water Algae in the water

Triboluminescence The production of light when certain crystals/materials are crushed or rubbed together Examples: Quartz Wintergreen candy