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Producing Visible Light

Section 10.2

Pgs. 394-398

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Producing Visible Light

Sources of Light

Hmm… Does the moon produce natural light? What do you think?

Incandescent Light

Incandescent light is produced by an object that is at a very high temperature.
Electric current flows through the metal filament causing it to glow and emit light.
Very inefficient. Only 5% of the electric energy is converted into light. Most of the energy is released as heat.

Fluorescent Light

Fluorescent light is emitted by some substances when they are exposed to electromagnetic radiation.
The bulb is filled with mercury vapour and coated with phosphor (white powder that glows when exposed to energized particles).
Electric current passes through the bulb causing the gas inside to glow.
More efficient, but still releases 80% of their energy as heat.

Chemiluminescence

Chemiluminescence is light produced from a chemical reaction without a rise in temperature.
This is referred to as `cool light` because it gives off very little heat.
All forms of bioluminescence are special kinds of chemiluminescence.

The ability of a plant or animal to produce light is called bioluminescence.
Some algae, jellyfish, insects, crustaceans, bacteria, earthworms, and fungi produce light.

Bioluminescence

Phosphorescent Light (glow-in-the-dark)

Phosphorescence is the ability to store energy from a light source and then emit it slowly over a long period.
The light eventually fades, but can be re-energized if held close to a light source.

Triboluminescence

Electric Discharge

Electric discharge is a method of producing light in which an electric current passes through the air or another gas (neon).
Lightning is an example of electric discharge through the air.
Neon lights produce light by discharging electricity through the element neon causing to glow intensely.

Light-Emitting Diode (LED)

Electroluminescence is the process of transforming electrical energy directly into light energy.
A light-emitting diode (LED) is an electroluminescent light source made out of a material called a semiconductor.
A semiconductor is a material that can be made to change how well it conducts electricity.

Some semiconductors can be made to emit light when a small electric current is passed through them.
Light-emitting diodes provide the backlight for many handheld devices.
Even more energy efficient than fluorescent light and take far less time to light up.

Plasma Displays

In a plasma display, each colour is a tiny fluorescent light in which an electrical signal causes a gas (such as neon) to illuminate as red, green, and blue light.
By varying the brightness of each primary colour, millions of colours can be produced.

Organic Light-Emitting Display (OLED)

An organic light-emitting display (OLED) is a light source made of several extremely thin layers of organic molecules that use an electric current to produce light.
OLEDs use less energy that other displays because they do not require a backlight, they are thinner, lighter, brighter, and more flexible.
OLED technology is new and has potential applications to screens of electronic devices, TV screens and computer screens.

Liquid Crystal Displays (LCD)

In liquid crystal display (LCD), a white light shines behind a liquid crystal.
A liquid crystal is a solid that can change the orientation of its molecules (like a liquid), but only when electricity is applied.
Electric current causes the liquid crystal to alter their positioning which emits light.
Special filters, called polarizing filters, are placed in front of the crystals to produce any colour of light.

Seatwork / Homework