LED (light-emitting diode)

A modern light source that requires low voltages is the LED. LEDs are typically used as on/off indicator lights in electrical appliances such as televisions, VCR’s, video cameras, computers, and stereos. They are also used to display numbers in some alarm clocks, radios, and microwave ovens. Another use is very large video displays at sporting events and concerts.

The chip at the heart of the LED consists of a p-n junction --- two different solid materials that have been joined together. It is surrounded by a transparent, hard plastic that protects the LED from vibration and shock. The LED is constructed in such a way that the light emitted by the chip is reflected off the base it sits on and is focused through the top of the LED. Thus, the light is brightest at the top of LEDs.

The two wires extending below the LED epoxy enclosure, or the "bulb" indicate how the LED should be connected into a circuit. The negative side of an LED lead is indicated in two ways:

by the flat side of the bulb, and

by the shorter of the two wires extending from the LED. The negative lead should be connected to the negative terminal of a battery. LED's operate at relative low voltages between about 1 and 4 volts, and draw currents between about 10 and 40 mill amperes. Voltages and currents substantially above these values can melt a LED chip.

The most important part of a LED is the semi-conductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges, and the n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons cross he junction into the p region.

LEDs are poised to make dramatic reduction in global energy consumption:

The US Department of Energy estimates potential global savings of $100B/yr and corresponding reductions of carbon emissions of 200 million tons/yr by 2025.

By 2025, 50% efficient LEDs could cut global lighting energy usage by 50% and total electricity usage by 10%.

LED Monitor / LED Television (TV LED)

The Impact of High Dynamic Range (HDR) Displays on LED Demand is high. LCDs and projection displays can’t even match the dynamic range of cinema, much less that of the real world. The goals of HDR are therefore as follows:

Use the full gray level and contrast capability of the display, especially in dark and bright images
Achieve darker blacks, brighter whites and the use of all gray levels
Improve color contrast and gray-level resolution
Reduce power consumption.