Sources of LightSNC2P – 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