ICT

 Hi! This term we are going to do another explanation about ICT, is to say, technology in general. We had a lot of options to choose but I went for LED technology. I don't know why. In fact, I first wanted to do protect data but I waited too much and a girl, called Paula, chose it, so I did LED. I find it very interesting; something whose importance is enormous and we use it everyday.

I'm now searching for some information about this topic and I have to say that there's a lot. Here you have some web pages:

- http://www.lighting.philips.com/main/education/lighting-university/lighting-university-browser/course/understanding-of-led-technology

- http://ecmweb.com/basics/understanding-led-technology

- http://www.edisontechcenter.org/LED.html

- https://es.slideshare.net/robcohen/led-lighting-presentation

- https://en.wikipedia.org/wiki/Light-emitting_diode#Advantages 

- http://sciencewithkids.com/science-facts/facts-about-LEDs.html

Reading these pages I finally did a brainstorm that I can follow to do my presentation:

Definition

A light-emitting diode (LED) is a special kind of diode that glows when electricity passes through it. Most LEDs are made from a semi-conducting material called gallium arsenide phosphide.
LEDs can be bought in a range of colours. They can also be bought in forms that will switch between two colours (bi-colour), three colours (tri-colour) or emit infra-red light.
In common with all diodes, the LED will only allow current to pass in one direction. The cathode is normally indicated by a flat side on the casing and the anode is normally indicated by a slightly longer leg. The current required to power an LED is usually around 20 mA.

Advantages:

• Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
• Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs.
• Size: LEDs can be very small (smaller than 2 mm²) and are easily attached to printed circuit boards.
• Warmup time: LEDs light up very quickly. A typical red indicator LED achieves full brightness in under a microsecond. LEDs used in communications devices can have even faster response times.
• Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.
• Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. 
• Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.

 

 




Disadvantages:

•  Initial price: LEDs are currently slightly more expensive (price per lumen) than other lighting technologies.
• Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment. Overdriving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure.
• LEDs must be supplied with the correct voltage and current at a constant flow. This requires some electronics expertise to design the electronic drivers.

History / inventors

1907 - H.J. Round discovered electroluminescence when using silicon carbide and a cats whisker. Oleg Losev independently discovered the phenomena the same year.
London, United Kingdom

	1920s - Oleg V. Losev studied the phenomena of light emitting diodes in radio sets. His first work on 'LEDs' involved a report on light emission from SiC. In 1927 he published a detailed report but his work was not well known until the 1950s when his papers resurfaced. Saint Petersburg, Russia
	1961 - James R. Biard. "Bob" Biard and Gary Pittman developed the Infrared LED at Texas instruments. This was the first modern LED. It was discovered by 'accident' while TI tried to make an X-band GaAs varactor diode. The discovery was made during a test of a tunnel diode using a zinc diffused area of a GaAs (Gallium Arsenide) semi-insulating substrate. Dallas, Texas
	1961 - Gary Pittman worked together with James R. Biard. He had started working in 1958 with semiconductor GaAs for the creation of early solar cells. He discovered and developed the infrared LED with James R. Biard. Dallas, Texas
	1962 - Nick Holonyack Jr. develops the red LED, the first LED of visible light. He used GaAsP (Gallium Arsenide Phosphide) on a GaAs substrate. General Electric. Syracuse, New York
	1972 - M. George Craford creates the first yellow LED at Monsanto using GaAsP. He also develops a brighter red LED. St. Louis, Missouri
	1972 - Herbert Maruska and Jacques Pankove develop the violet LED using Mg-doped GaN films. The violet LED is the foundation for the true blue LED developed later. RCA Labs , New Jersey
	1979 - Shuji Nakamura develops the world's first bright blue LED using GaN (Gallium nitride). It wouldn't be until the 1990s that the blue LED would become low cost for commercial production. Tokushima, Japan
	1976 - Thomas P. Pearsall develops special high brightness LEDs for fiber optic use. This improves communications technology worldwide. Paris, France

How does it work?

Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called photons, are the most basic units of light.
Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Electrons in different orbitals have different amounts of energy. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.

How much do we use them?



Uses ( different examples )



 



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