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Lighting basics

LED Basics

Unlike incandescent and fluorescent lamps, LEDs are not inherently white light sources. Instead, LEDs emit nearly monochromatic light, making them highly efficient for colored light applications such as traffic lights and exit signs. However, to be used as a general light source, white light is needed. White light can be achieved with LEDs in three ways:

Phosphor conversion, in which a phosphor is used on or near the LED to convert the colored light to white light;
RGB systems, in which light from multiple monochromatic LEDs (red, green, and blue) is mixed, resulting in white light; and
A hybrid method, which uses both phosphor-converted and monochromatic LEDs.

The potential of LED technology to produce high-quality white light with unprecedented energy efficiency is the impetus for the intense level of research and development currently supported by the U.S. Department of Energy

The potential of LED technology to produce high-quality white light with unprecedented energy efficiency is the impetus for the intense level of research and development currently supported by the U.S. Department of Energy

Colour Rendering

Colour rendering relates to the way objects appear under a given light source. The measure is called the "colour rendering index" or CRI. A low CRI indicates that objects may appear unnatural under the source, while a light with a high CRI rating will allow an object's colours to appear more natural. The maximum value of the CRI of a source is equal to 100. The higher the value, the better the colour rendering is. Light sources providing a CRI over 80 are considered as excellent for colour recognition.

Colour Temperature

A specification of the colour appearance of a light source, relating the colour to a reference source (Planckian radiator) heated to a particular temperature, measured in Kelvin.

The CIE chromaticity diagram shows the evolution of this Plankian radiator (also called a black body radiator) through the different colours of the diagram.

Color temperatures over 5,000K are called cool colors (bluish white), while lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red).[1] This relation, however, is a psychological one in contrast to the physical relation implied by Wien's displacement law, according to which the spectral peak is shifted towards shorter wavelengths (resulting in a more blueish white) for higher temperatures

Luminous Intensity

Luminous intensity is the concept for the concentration of light in a specific direction, radiated per second.
It is designated by the symbol I. The unit is the candela (cd).
The luminous intensity can be defined as:
The luminous flux in a certain direction, radiated per unit of solid angle.

1 candela = 1 lumen / steradian


Intensity is not a function of distance

The photometrical performances of a luminaire are derived from the luminaire’s measured luminous intensity distribution. These measurements of luminous intensity are carried out in specialised laboratories, using goniophotometers

Luminous Flux

In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light), in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.

Luminous flux is the total quantity of light energy emitted per second by a light source.  It is designated by the symbol F and is expressed in lumens.   Luminous flux measurement of artificial light sources is carried out within a perfectly diffusing white sphere, called an Ulbricht sphere.  This equipment measures the total amount of lumens emitted by the tested light source by comparison with a calibrated lamp.

Top 8 Things You Should Know About LEDs

8. A
light-emitting diode, or LED, is a type of solid-state lighting that uses a semiconductor to convert electricity into light. Today’s LED bulbs can be six-seven times more energy efficient than conventional incandescent lights and cut energy use by more than 80 percent.

7. Good-quality LED bulbs can have a useful life of 25,000 hours or more -- meaning they can last more than 25 times longer than traditional light bulbs. That is a life of more than three years if run 24 hours a day, seven days a week.

6. Unlike incandescent bulbs -- which release 90 percent of their energy as heat -- LEDs use energy far more efficiently with little wasted heat.

5. From traffic lights and vehicle brake lights to TVs and display cases, LEDs are used in a wide range of applications because of their unique characteristics, which include compact size, ease of maintenance, resistance to breakage, and the ability to focus the light in a single direction instead of having it go every which way.

4. LEDs contain no mercury, and a recent Energy Department study determined that LEDs have a much smaller environmental impact than incandescent bulbs. They also have an edge over compact fluorescent lights (CFLs) that’s expected to grow over the next few years as LED technology continues its steady improvement.

3. Since the Energy Department started funding solid-state lighting R&D in 2000, these projects have received 58 patents. Some of the most successful projects include developing new ways to use materials, extract more light, and solve the underlying technical challenges. Most recently, the Energy Department announced five new projects that will focus on cutting costs by improving manufacturing equipment and processes.

2. The first visible-spectrum LED was invented by Nick Holonyak, Jr., while working for GE in 1962. Since then, the technology has rapidly advanced and costs have dropped tremendously, making LEDs a viable lighting solution. Between 2011 and 2012, global sales of LED replacement bulbs increased by 22 percent while the cost of a 60-watt equivalent LED bulb fell by nearly 40 percent. By 2030, it's estimated that LEDs will account for 75 percent of all lighting sales.

1. In 2012, about 49 million LEDs were installed in the U.S. -- saving about $675 million in annual energy costs. Switching entirely to LED lights over the next two decades could save the U.S. $250 billion in energy costs, reduce electricity consumption for lighting by nearly 50 percent and avoid 1,800 million metric tons of carbon emissions.