Producing Visible Light

Lesson 2 November 2nd, 2010

`• The most important source of light is the Sun. Other

natural sources of light, are stars, fire, and lightning.

Bioluminescence• The ability of a plant or animal to produce

light is called

• 90 percent of all sea creatures are bioluminescent

• Some fish produce their own light, while others have bacteria that carry out the light-producing chemical reaction for them.

Bioluminescence• Light can be used to attract prey, provide

camouflage, and keep schools together.

• On land various animals use light to attract mates. Example: Firefly

• Some Fungi and bacteria can also produce light

Incandescent Light

• Produced light at a very high temperature.

• Inside an incandescent light bulb is a tungsten filament

• Electric current heats it to an extremely high temperature.

Incandescent Light

• The filament emits light as a way to release energy. The light is the filament glowing.

• Incandescent bulbs are extremely inefficient. • Only 5 percent of the electrical energy used is

converted to light. The rest is heat.

Fluorescent Light• Light emitted by substances when they are

exposed to (ultraviolet) radiation.

• A fluorescent light bulb is filled a gas such as mercury vapour.

• The bulb is coated with a white powder called a phosphor.

Fluorescent Light

• When ultraviolet radiation strikes the phosphor, it emits light.

• Compact fluorescent light bulbs use 20% of the energy in light. The rest is heat

Phosphorescent Light• Some substances have the ability to store energy

from radiation.

Phosphorescent Light• Phosphorescence is the ability to store energy then

emit it slowly over a long period.

• Phosphorescent materials glow in the dark for some time after being energized by light

Chemiluminescence• Light produced from a chemical reaction without a rise in

temperature.

• All forms of bioluminescence are special kinds of chemiluminescence.

• Example: Glow sticks

Chemiluminescence• Chemiluminescence is also used in analyzing

crime scenes. Investigators use a chemical called luminol to detect

• traces of blood because the chemical glows when it reacts with the iron found in blood

Triboluminescence• Producing light from friction

• Some crystals can be made to glow simply by rubbing them together or crushing them.

Electric Discharge• The process of producing light by passing an

electric current (electrons) through a gas

• Example: Neon lights, Lightning, Carbon arcs, HIDs

Light-Emitting Diode (LED)

• The process of transforming electrical energy directly into light energy is called electroluminescence.

• A light-emitting diode (LED) is an electroluminescent light source made out of a material called a semiconductor.

• Allows positive and negative charged particles come together to release energy (light)

Light-Emitting Diode (LED)

• since solid materials are used, they are very rugged

• LEDs are very efficient producers of light • Uses: electronic billboards, traffic lights,

decorative lights, and handheld displays.