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Sources of Light

A variety of light sources are discussed for SNC2D

David Spencer

on 4 February 2011

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Transcript of Sources of Light

Light Sources Incandescent Light produced by an object, such as a metal, that is at a very high temperature
Involves a filament, which is a thin piece of wire. Electric current heats the filament to an extremely high temperature.
The filament emits light as a way to release some of its energy.
Incandescent bulbs are extremely inefficient. Only 5 percent of the electrical energy used in an incandescent light bulb is converted to light. The rest of the energy is released as heat.
Because they waste more energy than fluorescent lights, incandescent bulbs are being eliminated from widespread use. Fluorescent Light emitted by some substances when they are exposed to electromagnetic radiation.
A fluorescent light bulb is a glass tube filled with a small amount of a gas such as mercury vapour.
The inside of the bulb is coated with a white powder called a phosphor which is a substance that glows when exposed to energized particles.
As electric current passes through a fluorescent bulb, it energizes the atoms in the gas, which then emit ultraviolet radiation.
The ultraviolet radiation strikes the phosphor on the inside of the bulb, which then glows and emits light.
Compact fluorescent light bulbs are much more efficient than incandescent light bulbs, but they still release up to 80 percent of their energy as heat. Phosphorescent Light Phosphorescence is the ability to store the energy from a source of light and then emit it slowly over a long period.
Phosphorescent materials glow in the dark for some time after being energized by light.
The light from glow-in-the-dark objects eventually fades, but it can be re-energized if the object is held close to a light source for a few minutes. Chemiluminesence is light produced from a chemical reaction without a rise in temperature.
Because the chemical reaction gives off very little heat, the light produced is sometimes referred to as cool light.
All forms of bioluminescence are special kinds of chemiluminescence.
An example of chemiluminescence is the light produced in glow sticks.
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. Producing light from friction is called triboluminescence. Some crystals can be made to glow simply by rubbing them together or crushing them.
The Ute Aboriginal people of Utah and Colorado traditionally made ceremonial rattles containing 30 pieces of quartz.
The rattle was made of thin buffalo hide to permit flashes of light to pass through.
Triboluminescence can also be produced by breaking apart sugar crystals or rubbing a diamond. Triboluminescence. Electric Discharge an electric current passes through the gas, such as neon.
Lightning is one example of an electric discharge.
carbon-arc light sources can be used to produce searchlights with beams so powerful that their light can reflect off of the bottoms of high clouds.
A carbon-arc light involves passing an electric current through the air, or another gas, between two carbon rods. Light Emitting Diode The process of transforming electrical energy directly into light energy is called electroluminescence.
Electroluminescent devices consume much less energy than sources such as fluorescent devices.
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. OLED a light source made of several extremely thin layers of organic molecules
uses an electric current to produce light. An
is made of thousands of individual organic light-emitting diodes that use different organic molecules to emit different colours of light.
use less energy than some other displays because they do not require a backlight to function.
They are thinner, lighter, brighter, and more flexible.
In fact, they are so flexible that OLEDs can be rolled up or embedded in fabrics or clothing. Plasma used by many large-screen televisions
can produce brighter images than an LCD display
requires much more electrical power to operate.
each colour is a tiny fluorescent light in which an electrical signal causes a gas, such as neon, to release ultraviolet radiation.
The ultraviolet radiation is absorbed by phosphors that then radiate light in the visible spectrum.
Different phosphors are used to produce red, green, and blue light.
By varying the brightness of each primary colour, millions of colours can be produced. Liquid Crystal Display used by laptop computers, digital watches, cellphones, iPods, and many flat-panel television
a white light, such as a fluorescent light or lightemitting diode, 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.
The crystal can block light or transmit light depending on how much electricity is applied to it.
Red, green, and blue filters are placed in front of the crystal to produce these colours.
A special filter called a polarizing filter blocks the red, blue, or green colours in any combination to produce any colour of light.
Each tiny square of colour is called a pixel. Since liquid crystal displays work by blocking light, the white light that shines behind the crystals is always on, and just like blinds that cover a window, the crystal does not block all the light coming through.
For this reason, the black in LCDs does not appear completely black, but only dark grey.
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