When LED was invented?
LEDs were first developed in the 1960s but were used only in indicator applications until recently.
The electronics industry has used LED technology for several decades as indicator lights for various electronic devices. In more recent years, LED technology has progressed to the point where it is viable for general lighting applications.

Why LED's?
As a rule, LED bulbs use 90% less electricity than standard bulbs. They have an unparalleled even spectrum of light and have a lifespan beyond ten years. LED's provide us the most efficient way to save energy and conserve our natural resources. If LED's were implemented right now universally, we would not need to build another power plant. LEDs would actually eliminate the need for over 30 existing power plants!

How LED emit different color?
The specific wavelength or color emitted by the LED depends on the materials used to make the diode. Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP). "White" light is created by combining the light from red, green, and blue (RGB) LEDs or by coating a blue LED with yellow phosphor.

What’s Low Power LEDs?
Low power LEDs commonly come in 5 mm size, although they are also available in 3 mm and 8 mm sizes. These are fractional wattage devices, typically 0.1 watt, operate at low current (~20 milliamps) and low voltage (3.2 volts DC), and produce a small amount of light, perhaps 2 to 4 lumens.

What’s High Power LEDs?
High power LEDs come in 1-3 watt packages. They are driven at much higher current, typically 350, 700, or 1000 mA, and—with current technology—can produce 40-80 lumens per 1-watt package.

Where have LEDs been used in the lighting industry?
LEDs are commonly used in aesthetic, effect, or specialty lighting applications, including architectural highlighting.
Most traffic lights and exit signs, for example, now use red, green or blue LEDs.

Have LEDs always been used in general illumination lighting?
No. Early attempts to apply LEDs in general illumination lighting failed because they didn't meet the lumen-per-watt output or color requirements.
Technology has advanced to the point where using LEDs for general illumination is now viable.
Lighting industry experts are gaining a better understanding of how to capitalize on that technology.

Why have past attempts to create general illumination LEDs failed?
Conventional approaches to developing general illumination LEDs often involved retrofitting existing fixtures to house the new LED technology.
Instead of investigating the benefits and challenges of LEDs, many early attempts simply used traditional lighting standards and housings.
The problem was that LED technology breaks all traditional rules, and it quickly became apparent that old thinking couldn't be applied to this new technology.
Long-term research and development goal calls for white-light LEDs producing 160 lm/W in cost-effective, market-ready systems by 2025. In the meantime, how does the luminous efficacy of today's white LEDs compare to traditional light sources? Currently, the most efficacious white LEDs can perform similarly to fluorescent lamps. However, there are several important caveats, as explained below.

Why don't LEDs function as efficiently in a traditional fixture housing?
An LED module may physically fit into an existing housing, but that housing doesn't leverage the inherent qualities of the LEDs. Standard housings can't handle the challenges of LED thermal management, which is vastly different than thermal management for traditional incandescent or fluorescent lighting. Also, the optical design used in most traditional fixtures doesn't maximize the LED's efficiency.

What are the advantages to using LED lights?
LEDs bring several advantages to the lighting industry, including high efficiency and durability, and, with superior life over other lamp sources, their required maintenance is greatly reduced. This translates into energy savings, maintenance savings and an overall reduction in cost of ownership over the product's lifetime.

Do I have to replace LED diodes?
An LED does not burn out like a standard lamp, so individual diodes do not need to be replaced. Instead, the diodes gradually produce lower output levels over a very long period of time. If one LED fails, it does not produce a complete fixture outage.

What’s Phosphor Conversion?
Phosphor conversion is a method used to generate white light with LEDs. A blue or near-ultraviolet LED is coated with a yellow or multichromatic phosphor, resulting in white light.

What’s Luminous efficacy?
Luminous efficacy is typically used measure of the energy efficiency of a light source. It is stated in lumens per watt (lm/W), indicating the amount of light a light source produces for each watt of electricity consumed.
For white high-brightness LEDs, luminous efficacy published by LED manufacturers typically refers to the LED chip only, and doesn't include driver losses.

What’s CCT?
Correlated color temperature (CCT) is the measure used to describe the relative color appearance of a white light source. CCT indicates whether a light source appears more yellow/gold/orange or more blue, in terms of the range of available shades of "white." CCT is given in kelvins (unit of absolute temperature). See more information in the Color Quality section.

What’s CRI?
Color rendering index (CRI) indicates how well a light source renders colors of people and objects, compared to a reference source.

What's the difference between efficiency and efficacy?
Efficacy is a term normally used in cases where the input and output units differ. In lighting, we are concerned with the amount of light (in lumens) produced by a certain amount of electricity (in watts).
On the other hand, efficiency is a term that is typically dimensionless. For example, lighting fixture efficiency is the ratio of the total lumens exiting the fixture to the total lumens initially produced by the light source.

Efficiency or efficacy?
The term "efficacy" normally is used where the input and output units differ. For example in lighting, we are concerned with the amount of light (in lumens) produced by a certain amount of electricity (in watts). The term "efficiency" usually is dimensionless. For example, lighting fixture efficiency is characterized as a ratio of the total lumens exiting the fixture to the total lumens produced by the light source. "Efficiency" is also used to discuss the broader concept of using resources efficiently.

Lumen:
The SI unit of luminous flux. The total amount of light emitted by a light source, without regard to directionality, is given in lumens.

Luminaire efficacy:
The total luminous flux emitted by the luminaire divided by the total power input to the luminaire, expressed in lm/W.

What’s general illumination?
General illumination is a term used to distinguish between lighting that illuminates tasks, spaces, or objects from lighting used in indicator or purely decorative applications. In most cases, general illumination is provided by white light sources, including incandescent, fluorescent, high-intensity discharge sources, and white LEDs. Lighting used for indication or decoration is often monochromatic, as in traffic lights, exit signs, vehicle brake lights, signage, and holiday lights.

What's Energy efficiency?
Energy efficiency of light sources can be characterized in several different ways. Luminous efficacy indicates how much light the source provides per watt of electricity consumed. This is stated in lumens per watt (lm/W). Another measure of energy efficiency is the total watts a device consumes in providing the intended service.