SNC2DOptics Unit Half Notes
Sources of Light
•All objects that we see are sources of light, even if they do not produce light themselves.
•Objects that produce light are said to be .
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•Most objects do not produce light on their own. Objects are
•Coloured liquids and stained glass windows allow light to pass through them and this allows us to see the objects.
•Objects that we see because light reflects from them or passes through them are called .
•Non-luminous objects are sometimes referred to as
•Luminous Sources of Light can be both
•Natural sources of light are those that produce light
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•Artificial sources of light are those that are
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•Some sources of light, such as burning wood, may be classified as both natural and artificial.
•Light is produced when other forms of energy (heat or chemical) are converted into light energy.
•Luminous objects produce light are:
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Incandescent
•When steel is heated to temperatures over 2000 degrees Celsius, it gives off white light.
•A substance that gives off light because it has been heated
•Substances can be heated to incandescence by electricity.
•The light from a household light bulb is produced by heating a fine coil of tungsten wire (filament) until the temperature rises and gives off a bright light.
•These bulbs are called incandescent bulbs.
•The space inside an incandescent light bulb is filled with nitrogen or argon.
•If the space was filled with oxygen, the gas would react with the hot filament.
Electric Charge
•When an , light is sometimes produced.
•A natural occurrence of this is .
•Another natural example of this is the
•An artificial way of producing light .Other gases are used to produce different colours.
Fluorescence
•Fluorescence occurs when .
•A fluorescent light makes use of both electric discharge and fluorescence.
•A fluorescent light tube is filled with low pressure mercury vapour. The inner surface of the tube is coated with a fluorescent material.
•When an electric current is passed through the vapour, UV light is produced. The UV light hits the powder, which then produces visible light.
•A fluorescent tube is much more efficient than a regular incandescent light bulb.
•About 20% of the electrical energy used in a fluorescent light is converted to visible light, but only 5% of the electrical energy used in an incandescent bulb is converted to visible light.
•If you place you hand near a fluorescent tube, it feels cool. If you place you hand near an incandescent bulb, it feels warm.
Phosphorescent
•When a fluorescent tube is switched off, no more UV light is produced and the coating stops giving off light.
•Some fluorescent substances though, continue to give off light for hours after the energy source has been removed. These substances are called .
•Luminous dials on watches, .
CFL Bulbs
•Governments around the world recommend that homes and businesses switch to
•CFL bulbs than an incandescent bulb and
•CFLs than an incandescent bulb and the mercury in the CFLs can cause environmental pollution.
•All used fluorescent bulbs should be taken to a hazardous waste collection site.
•CFLs were devised to reduce the length of regular fluorescent light fixtures.
Chemiluminescence
•Light can be the result from the energy released in The products of the chemical reaction give off visible light. This process is called
Bioluminescence
•Some living things can make themselves luminous .
•Many organisms that live deep in the ocean use bioluminescence because so little sunlight reaches far below the surface of the water.
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Triboluminescence
•Troboluminescence is the production of light when certain crystals are scratched, crushed, or rubbed.
•The light emitting Diode is a very efficient light producing technology.
•An electric current passes through an LED, it emits light.
•LEDs save energy, last longer and stay cooler than Incandescent bulbs of CFL bulbs.
•The light emitting Diode is a very efficient light producing technology.
•An electric current passes through an LED, it emits light.
•LEDs save energy, last longer and stay cooler than Incandescent bulbs of CFL bulbs.