LIGHT ENERGY & ITS SOURCES Section 10.1

Discuss the following and are ready to give answers when prompted: In groups Discuss the following and are ready to give answers when prompted: What are the sources of light? How does a light bulb work? What does luminous and non-luminous mean? How is a shadow formed? What does transparent, translucent and opaque mean? Electricity passes through the filament and its starts to get hot and glows. GIVES OFF LIGHT (EMITS) REFLECTS LIGHT A SOLID OBJECTS BLOCK THE LIGHT Can see through can see some light light cant get through

Light Light is a form of energy that can be detected by the human eye Light energy comes from both natural and artificial sources Light travels directly from a luminous source (object that emit light) or indirectly from a non-luminous source (object reflects light) to your eyes

Electrical energy → light energy + thermal energy Incandescence Emitting light because of high temperatures Kerosene lamp uses chemical energy to transform into heat and light. electricity passes through a tungsten wire in a bulb making it so hot that it glows Inefficient - since much of the input energy becomes thermal (heat) energy Electrical energy → light energy + thermal energy

Luminescent an emission of light by a substance not resulting from heat

Electric Discharge Electric discharge is the process of emitting light because of electricity passing through a gas Examples: Lightning, neon signs

Phosphorescence Materials called phosphors store light energy and release it again as light energy Phosphorescence is the process of emitting light for a short time after receiving energy from another source

Fluorescence Fluorescence is the process of emitting light while receiving energy from another source Ex. Fluorescent light tubes Fluorescence is a combination of two different light sources, electric discharge and phosphorescence Electricity passes along the tube and causes particles of mercury vapour to emit invisible ultraviolet (UV) energy. The UV energy is absorbed by the phosphor coating on the inside of the tube, which then emits light energy.

Chemiluminescence Chemiluminescence is the process of changing chemical energy into light energy with little or no change in temperature

Bioluminescence Bioluminescence is when chemiluminescence is used in living things

Luminescent Incandescent Visible Light Luminescent (emits light without heat) Incandescent (emit light because of heat) Phosphorescent Chemiluminescent Candlelight Electric Discharge Glow-in-dark stickers Bioluminescent neon signs Fluorescent firefly glow sticks fluorescent bulbs Activity: Create a concept map of the different sources of light breaking them down from visible light to examples.

Sources of Light What factors should be considered when choosing a light source? Brightness Location Attractiveness Cost Efficiency (how well the light source transforms input energy into light energy) Project: Create an advertisement promoting a source of light