WHAT IS LIGHT?

• Form of energy (first basic principle of light) that you can see

•Radiates (spreads out) in all directions

•Light travels in a straight line unless it hits something or is pulled by gravity

•Light can be converted to different forms of energy like heat (thermal), electricity, or

chemical energy (photosynthesis)

CONVERSION TO THERMAL ENERGY

• The greenhouse effect

Light energy enters the greenhouse, hits objects and gets converted to thermal

energy which can’t get back out so heat builds up

This is a good thing

Green house gases, eg, CO2, trap more of the sun’s energy

increasing global temperatures

Too much of a good thing =

GLOBAL WARMING

WHERE DOES LIGHT COME FROM? - SOURCES OF LIGHT

• Natural light comes from the sun

• Artificial light can come from a variety of sources

1. Incandescent

2. Phosphorescent

3. Fluorescent

4. Chemiluminescent

5. Bioluminescent

NATURAL LIGHT

Light from the sun is produced by billions of nuclear reactions producing unimaginable amounts of energy

Visible light is only one form of energy that the sun provides

Other forms of energy from the sun are invisible and include radio waves, infrared waves,

ultraviolet, x-rays and gamma rays

INCANDESCENT LIGHT

Examples are a candle flame

And an ordinary light bulb

Visible light is produced by heating something to an extremely high temperature

Electrical energy Thermal energy Visible light energy

Phosphorescent

Absorption of light and then that light is radiated back out later

Many glow in the dark toys are made with paints, dyes and inks that phosphoresce

Watch painted with phosphorescent ink

Same watch, lights out Same watch, about 10 minutes later

FLUORESCENTAn example of this type of light is the fluorescent light bulb

The special phosphor coating inside the bulb absorbs the

ultraviolet energy given off by the mercury gas

The phosphor coating then glows

with visible light energy

Much more efficient than an incandescent light

source because there is not as much heat

produced

THE NORTHERN LIGHTS – AURORA BOREALIS

Very fast moving electrons in solar winds coming from the sun enter the earth’s atmosphere and collide with gaseous

particles releasing energy in the form of light

CHEMILUMINESCENT

Energy for light comes from a chemical reaction

BIOLUMINESCENT

Fireflies

Marine animals

A cloud of bioluminescent

marine organisms seen from space

An aura given off by bioluminescent water organisms

Chemiluminescence in living organisms

LIGHTING TECHNOLOGY AND SOCIETY – LEDs

LED = light emitting diode

Light is generated by the energy given off as millions of tiny negatively charged

particles bounce around inside a small device called a diode

LEDs use less electricity, last longer and do not produce as

much heat as incandescent light bulbs

LIGHTING TECHNOLOGY AND SOCIETY – FIBRE OPTICS

Light is transmitted along bundles of tiny tubes

Inside the tiny tubes, light cannot escape, it is constantly internally reflected

Telephone signals

Cable signals

Internet signals