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 energyThermal energyVisible 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

FLUORESCENT An 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