Basic knowledges on LED lights:
* LEDs - light emitting diodes – have been popular for some years as indicator lights. More than you probably realise, these little lights are everywhere in your every day life: there is the red light of your digital clock at night, the green light from your cell phone display, … LEDs are all around us.

* LEDs are solid-state devices that convert electric energy directly into light of a single color. Because they employ “cold” light generation technology, in which most of the energy is delivered in the visible spectrum, LEDs don't waste energy in the form of non-light producing heat.

* LED light or LED lamp is a type of solid state lighting that uses light-emitting diodes(LEDs) as the sources of light. They usually comprise clusters of LEDs in a suitable housing. They come in different shapes, including the standard light bulb shape with a large E27 Edison screw and MR16(GU5.3) shape with a bi-pin base, as well as small E14 Edison screw and GU10 bayonet socket.

Advantages of LED lights:
-High efficiency - LEDs are now available that reliably offer over 100 lumens from a one-watt device, 
 or much higher outputs at higher drive currents.
-High durability - no filament or tube to break like traditional incandescent lamp or fluorescent lamps.
-Long life span - in properly engineered lamps, LEDs can last 50,000-60,000hours or above.
-Low power consumption
-Low heat emission - LEDs produce cold lighting source which make less lighting pollution and less heat
  emission.
-Environmental protection - unlike fluorescent and most HID lamps, LED lights contain no hazardous mercury or
  halogen gases.
-Full dimmablility - ulike fluorescent lamps, LEDs can be dimmed using pulse-width modulation(PWM -
  turning the light on and off very quickly at varying intervals), this also allow full color mixing in lamps with LEDs of 
  different colors.
-Different Colors - LEDs have optional colors for decorative lighting which makes the world beautiful.

Main Applications of LED lights:
-Automotive lighting
-Bicycle ligthing
-Billboard displays
-Domestic lighting for decoration
-Display lighting in art galleries to achieve a low heating effect on pictures etc.
-Flashlight or electric torches
-Floodlighting of buildings
-State lighting
-Traffic lights
-Train light and Railway signals

Technical Parameters for LED Light
Luminious Energy
Luminous energy is the perceived energy of light. This is cometiomes also called the quality of light.

Luminous flux (lm)
Luminous flux or luminous power is the measure of the perceived power of light. The SI unit of luminous flux is the lumen(lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian.

Luminous Intensity (cd)
Luminous intensity is a measure of the wavelength-weighted power emitted by a light sources in a particular direction per unit solid angle, based on the luminosity function, a standardized moel of the sensitivity of the human eye. The SI unit of luminous intensity is the candela(cd).

Luminance (cd/m2)
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes throught or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square meter cd/m2.

Luminous Efficacy (lm/W)
Luminous efficacy is a figure of merit for light sources. It is the ratio of luminous flux (in lumens) to power(usually measured in watts). As most commonly used, it is the ratio of luminous flux emitted from a light sources to the electric power consumed by the source, and thus describes how well the source provides visible light from a given amount of electricity. This is also referred to as luminous efficacy of a source. In SI, luminous efficacy has units of lumens per watt(lm/W).

Illuminance(lx)
Illuminance is used in photometry as a measure of the apparent intensity of light hitting or passing throught a surface. It is analogous to the radiometric unit watts per square meter, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human brightness perception.The SI unit of illuminance is lux(lx). Lux is derived unit based on lumen, and lumen is based on candela.

SI photometry units

Quantity Symbol SI Unit Abbr. Remarks 
Luminous Energy Qv lumen second lm·s units are sometimes called "talbots"
Luminous Flux F lumen (= cd·sr lm also called "luminous power"
Luminous Intensity Iv candela(=lm/sr) cd an SI base unit
Luminance Lv candela per square meter cd/m2 units are sometimes called "nits"
Illuminance Ev lux (= lm/m2) lx used for light incident on a surface
Luminous Emittance Mv lux (= lm/m2) lx used for light emitted from a surface
Luminous Efficacy   lumen per watt lm/W ratio of luminous flux to radiant flux


Wavelength
In physics, wavelength is the distance between repeating units of a propagating wave of a give frequency. The wavelength is related to the frequency by the formula: wavelength=wave speed/frequency.

Color Temperature
Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, and other fields. The color temperature of a light sources is determined by comparing its chromaticity with that of an ideal black-body radiator. The temperature, usually measured in kelvins(K) at which the heated black-body radiator matches the color of the light source is that source's color temperature, for a black body source, it is directly related to Planck's law and Wien's displacement law.

Counterintuitively, higher color temperatures (5000K or more) are "cold"(green-blue) colors, and lower color temperatures(2700-3500K) "warm"(yellow-red) colors.

2700-3500K) "warm"(yellow-red) colors.
 
 
Categorizing different lighting
Temperature Source
1700K Match flame
1850K Candle flame
2700–3300K Incandescent light bulb
3350K Studio "CP" light
3400K Studio lamps, photofloods, etc.
4100K Moonlight, xenon arc lamp
5000K Horizon daylight
5500–6000K Typical daylight, electronic flash
6500K Daylight, overcast
9300K CRT screen
Note:
These temperatures are merely approximations; considerable variation may be present.