10.2 Producing Visible Light

incandescent light - how do they work?

When you turn on the light bulb, an electric current flows through the filament (thin piece of wire), hearing it to an extremely high temperature; the filament emits light to release some of its energy

liquid crystal

a solid that can change the orientation of its molecules like a liquid, but only when electricity is applied

LED - efficiency

can replace incandescent and fluorescent lights (very efficient and radiate very little heat; last very long; work (light up) faster for ex. as rear brake lights)

LED - uses

electronic billboards, traffic lights, decorative lights, handheld displays

semi-conductor

electrons flow, but not quickly; can be made to change how well it conducts electricity; can be made to emit light when a small electric current is passed through them

phosphorescence

the ability to store the energy from a source of light and emit it slowly over a long period; glow in the dark for some time after being energized

electroluminescence

the process of transforming electrical energy directly into light energy

OLED - uses

thinner, lighter, brighter, and more flexible so they can be rolled up or embedded in fabrics/clothing; potential application in small screens (cellphones, medical equipment), and large screens (TVs, computers); more expensive and easily damaged by water, but design is being refined

fluorescent light - how do they work?

A fluorescent light bulb is a glass tube filled with a small amount of gas (such as mercury vapour). The inside of the bulb is coated with white powder called a phosphor. A phosphor is a substance that glows after being exposed to energized particles. As electric current passes through a fluorescent bulb, it energizes the atoms in the gas, which then emits UV radiation. When the UV radiation strikes the phosphor, it glows and emits light.

fluorescent light - efficiency

More efficient than incandescent, but still release 80% of energy as heat

incandescent light - efficiency and use

Only 5% of the electrical energy used is converted to light, and the rest is released as heat; they are being eliminated from widespread use

Plasma

large screen televisions use display to produce brighter images than LCDs, but require much more electrical power; each colour is a tiny fluorescent light in which an electrical signal causes a gas, such as neon, to release ultraviolet radiation, which is absorbed by phosphors which radiate visible light; different phosphors are used to produce red, green and blue; by varying brightness of primary colours, millions of colours are produced

LED

light emitting diode; an electroluminescent light source made of a semiconductor; LEDs do not have a filament; they are solid and rugged, containing no delicate parts; operate using small amounts of electricity; very efficient and radiate very little heat; last very long; work (light up) faster

natural light

light produced by the Sun or other stars

chemiluminescence

light produced from a chemical reaction without a rise in temperature: because of this, it is referred to as cool light; all forms of bioluminescence=special kinds of chemiluminescence; examples include glow sticks, analyzing crime scenes (chemical called luminol detects traces of blood because the chemical glows when reacting to irom

artificial light

light produced through human technology

LCD

liquid crystal display; laptops, digital watches, cellphones, iPods, flat-panel TVs use LCD; a white light, such as fluorescent light or LED, shines behind a liquid crystal; crystal can block or transmit light depending on the amount of electricity applied; red, gree, and blue filters are placedin front of crystals to produce; a polarizing filter blocks any combo of colours; each tiny square of colour is called a pixel; some LCDs work by blocking light, so the white light that shines behind crystals is always on; this does not block all light, so black is not completely black

electric discharge

method for producing light in which an electric current passes through the air or another gas, such as neon; example includes lightning

OLED

organic light-emitting display; a light source made of several very thin layers of organic molecules that use an electric current to produce light; made of thousands of diodes that use different organic molecules to emit different colours of light; do not require a backlight so use less energy

triboluminescence

producing light from friction; examples include crystals crushed, Quartz, sugar crystals, rubbing a diamond