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The basic knowledge of the LED

- Aug 27, 2016 -

Leds are taken from LightEmitting Diode abbreviation for three words, Chinese translated into "light-emitting diodes (leds), as the name implies light-emitting diodes (leds) is a kind of electric energy into light energy can be electronic device has the characteristics of the Diode. The different leds emit different wavelengths of light from the infrared to the ultraviolet, there are coated with phosphor powder on the blue leds, blue light into the white light of white LED.

  

LED color and process:

Manufacturing LED material is different, can produce with different energy photons, could help control the wavelength of light emitted by an LED, namely spectrum or color. First in the history of the LED material is used by arsenic (As) gallium (Ga), the positive PN junction voltage drop (VF, voltage) can be understood As a light or work for 1.424 V, light for the infrared spectrum. Another common LED material for phosphorus (P), gallium (Ga), the positive PN junction voltage of 2.261 V, light for the green light.


Based on these two kinds of material, the early LED industrial use GaAs1 - freely xPx material structure, in theory, can produce from infrared to the green light within the scope of any wavelength of LED, the subscript X represents the percentage of phosphorus instead of arsenic. General pressure drop through the PN junction can determine the wavelength of the LED color. One of the typical GaAs0.6 P0.4 red light LED, GaAs0.35 P0.65 orange light LED, GaAs0.14 P0.86 yellow light LED and so on. Due to manufacturing the gallium and arsenic, phosphorus element, so commonly known as the LED luminous tube for the three elements. And GaN (gallium nitride) blue leds, GaP of green light LED and GaAs infrared LED, luminous tube called two elements. And the latest technology is to use mixed aluminum (Al), calcium (Ca), indium (In) and nitrogen (N) of the four elements AlGaInN four element materials of the four elements of the LED, can cover all the visible light and part of the ultraviolet spectral range.

  

Luminous intensity:

The measuring unit of luminous intensity unit of illuminance (Lux Lux), luminous flux unit (lumens Lumen), unit of luminous intensity (candlelight Candlepower)

1 CD (candles) refers to the object of all radiation, freezing point temperature in platinum, luminous intensity per square centimeter one over sixty area. (before 2.2 cm in diameter, the quality of 75.5 grams of oil, candle, burning 7.78 grams per hour, the flame height is 4.5 cm, the luminous intensity along the horizontal direction)

1 l (lumens) refers to the candle light in the distance is 1 cm 1 CD, covers an area of 1 square centimeters of flux on the plane.

1 lux (lux) refers to the luminous flux 1 l evenly distributed on the 1 square meter area of the intensity of illumination.

General active luminous body USES unit of luminous intensity candlelight CD, such as incandescent lamp, LED, etc.; Reflection or transmission type object using lumen flux unit L, such as LCD projector etc. The illumination unit Lux Lux, commonly used in photography, and other fields. Three kinds of measurement unit is equivalent in value, but need to understand from different angles. For example, if a LCD projector brightness (flux) of 1600 lumens, the projection to the size of the total reflection screen to 60 inches (1 square meters), the intensity of illumination for 1600 lux, assuming that the light outlet is apart from the light source is 1 cm, light outlet area of 1 square centimeters, the luminous intensity of light outlet for 1600 CDS. The real LCD projector by the loss of light transmission, reflection, or pervious to light the wastage of the film and the uneven distribution of light, brightness will be discounted, generally 50% efficiency is a very good job.


 

In practical use, intensity calculation often use is relatively easy to surveying and mapping unit of data or to use. For LED display the active light using CD/m2 as a general unit of luminous intensity, and cooperate with the viewing Angle for the auxiliary parameter, the equivalent on the surface of the screen surface illumination unit lux; The numerical multiplication and screen the effective display area, get the whole screen on the best Angle of luminous intensity, assuming that the luminous intensity of each pixel in the screen in the appropriate space constant, this value can be considered was the luminous flux for the entire screen. General outdoor LED display must be more than 4000 CD/m2 brightness can only be in the sun have ideal display effect. Common indoor LED, the maximum brightness in 700 ~ 2000 CD/square metre.

A single LED luminous intensity is an unit with the CD, equipped with Angle parameters at the same time, the luminous intensity has nothing to do with the colour of the LED. The luminous intensity of single pipe range from a few mCD to tens of thousands of mCD. The luminous intensity of LED manufacturers have given refers to the LED at 20 ma shed light up, the best Angle of luminous intensity and center position on the biggest point. Encapsulate leds when the shape of the top of the lens and the LED chip from the top of the lens position determines the Angle and light intensity distribution of LED. In general the same LED Angle, the greater the maximum luminous intensity is smaller, but in the entire three-dimensional hemisphere on the cumulative flux constant.


  

When multiple leds is closely emissions rules, its luminous sphere will overlap, lead to the entire light-emitting flat luminous intensity distribution more uniform. When calculating the display luminous intensity, based on the perspective LED and LED emission density, will provide the biggest manufacturers of point light intensity value multiplied by 30% ~ 90%, average luminous intensity as single tube.

General LED light for a very long life, manufacturers are generally marked for 100000 hours, actually also should pay attention to the LED brightness decay cycle, such as most UR red tube used in automobile tail lights lit a dozen to a few hours later, the brightness is only half of the original. Brightness decay cycle had a lot to do with LED production craft of material, usually under the condition of the economic conditions permit should choose four elements LED brightness attenuation is relatively slow.

The color, white balance:

White is red, green and blue three color brightness proportion of mixture, when the brightness of the light green is 69%, the brightness of the red is 21%, the brightness of the blue was 10%, mixed color eye feel is pure white. But the LED red, green and blue three color chromaticity coordinates cannot be achieved due to the technological process of the effect of whole spectrum, and control the brightness of the primary color deviation include primary pigments, called color.

For full color LED display before color matching, in order to achieve the best brightness and the lowest cost, should try to choose color luminous intensity into roughly 3:6:1 proportion of LED device composed of pixels.

  

The white balance for three primary colors were synthesized under the same the gray value still is pure white.

Primary colors and primary colors:

Primary means to synthesis the basic color of all sorts of color. For red, green, and blue light in the primary, spectrum is illustrated below table, the table three vertices for the ideal color wavelengths. If there is a deviation, color is can synthesis area reduces, the color spectrum in the table will narrow triangles, from the visual Angle, the color will not only have a deviation, rich degree reduced.

Leds emit red, green and blue line according to their characteristics and different wavelengths is roughly divided into pure red, purple, orange, orange, orange, yellow, yellow green, pure green, green, blue, green, pure blue, blue, purple, orange, yellow, green, violet. Three primary colors of green, the most important, because the green accounted for 69% of white brightness, and the colour is horizontally arranged at the center of the table. So weighed in on the purity of color and the relationship between the price, green is considered the object.


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