11.2 Methods of Light Production

Luminous: An object which produces visible light Ex: candle, sun, flashlight, neon lights Non-luminous: An object which does not produce visible light; reflects or allows light to pass through allow us to see the object Moon, stained glass windows, coloured liquids, textbook, pen, etc.

Methods of Light Production Incandescence: Production of light as a result of high temperature Ex: Candle, incandescent light bulb

glass bulb Conducting wire tungsten filament inert gas (argon) electrical contact

How does an incandescent light bulb work? The light bulb produces light when the fine coil of tungsten (called a filament) is heated Temperature rises to ~2500°C when an electric current passes through it! Tungsten is used because other metals at this high of a temperature melts Incandescent lamps are very inefficient sources of light because most energy is lost as heat Filled with a non-reactive gas because a more reactive gas could combust

Fluorescence: Immediate emission of visible light as a result of absorption of ultraviolet light Ex: fluorescent lights

How does a fluorescent light bulb work? 1. A long cylindrical glass tube is filled with mercury vapour 2. Electrical current flows through the tube, from the electrode which donates electrons to the electrode which accepts electrons 3. As the current flows through the tube, it excites atoms of mercury 4. The excited mercury atoms produce ultraviolet light (which we cannot see) 5. The UV light strikes the fluorescent coating on the inside of the glass tube and releases visible light

How does a fluorescent light bulb work? Electrical contact Electron discharge Glass tubing Fluorescent coating Mercury (Hg) atoms Electrode (electron donor ) Electrode (electron acceptor) Visible light produced

Electric discharge: Production of light by passing an electric current through a gas Aurora borealis, lightning, neon signs

Phosphorescence: Production of light by absorbing UV light and emitting visible light over an extended period of time Ex: glow in the dark stickers which contain phosphors

Chemiluminescence: Direct production of light as a result of a chemical reaction Little or no heat is produced Ex: glowsticks

How does a glow stick work? Hydrogen peroxide solution is contained in a long, narrow glass tube in the middle of a plastic case Phenyl oxalate and a florescent dye are contained in the body of the plastic case The two chemicals mix, producing a chemical reaction when the glass tube in the middle is broken

Bioluminescence: A type of chemiluminescence where light is produced in living organisms as a result of a chemical reaction with little or no heat produced Some fungi, fireflies, anglerfish, “jack-o-lantern” mushroom, jellyfish

Triboluminescence: Production of light from friction as a result of scratching or rubbing certain crystals Ex: biting down on wint-O-green lifesavers, rubbing quartz crystals together, peeling sticky tape (who’da thunk?!?) Check it out: (triboluminescence in quartz crystals and sticky tape)

Light Emitting Diode: Light produced as a result of an electric current flowing in semi-conductors. Semi –conductors: material that allows electricity to flow in only one direction (ex: silicon) Ex: christmas lights, traffic lights, electronic indicators