What is Light Emitting Diode (LED) ? and some basic knowledge about light emitting diode
A, led Basics
LED Light Emitting Diode three words are taken from the abbreviation, Chinese translated as "light emitting diode", as the name suggests it is a light emitting diode can convert electrical energy into light energy electronic devices having diode characteristics. Currently different light-emitting diodes can be issued from the infrared to the blue between the different wavelengths of light, the current issue of purple and even ultraviolet light-emitting diodes also have been born. In addition to the blue LED coated with phosphor, the blue light into white light white LED.
LED color and Technology:
LED manufacturers of different materials, can be generated with different photon energies in order to control the wavelength of light emitted by the LED, i.e. spectra or color. History's first LED material used is arsenic (As) of gallium (Ga), the PN junction forward voltage drop (VF, can be understood as light or voltage) is 1.424V, the light emitted from the infrared spectrum . Another commonly used material for LED phosphorus (P) gallium (Ga), the PN junction forward voltage drop of 2.261V, the light emitted from the green light.
Based on these two materials, the early use of LED industry GaAs1-xPx material Tu-structure, in theory, can be produced from the infrared light has been to any wavelength in the green range of the LED, subscript X represents phosphorus elements replace the percentage of arsenic. Generally through the PN junction voltage drop can determine the wavelength of LED colors. Typical of these are GaAs0.6P0.4 red LED, GaAs0.35P0.65 orange light LED, GaAs0.14P0.86 yellow LED and the like. Due to manufacturing using gallium, arsenic, phosphorus three elements, commonly known as the three elements of these LED light tubes. And GaN (gallium nitride) blue LED, GaP green LED and GaAs infrared LED, is referred to as the second element. And the latest technology is mixed with aluminum (Al), AlGaInN calcium (Ca), indium (In) and nitrogen (N) of the four elements of the four elements the four elements of LED, can cover all the visible and ultraviolet part spectral range of light.
LED luminous intensity:
Luminous intensity measurement unit has illumination units (lux Lux), luminous flux units (lumens Lumen), luminous intensity unit (Candlelight Candle power).
1CD (candlelight) means full radiation objects, in platinum freezing point temperature, every sixtieth square cm area of luminous intensity. (Formerly refers to the diameter of 2.2 cm, mass of 75.5 grams of whale oil candle burning 7.78 grams per hour, the flame height of 4.5 cm in the horizontal direction of the luminous intensity)
1L (lumens) means 1 CD candlelight irradiation at a distance of 1 cm, an area of one square centimeter of flux plane.
1Lux (lux) means 1L the flux evenly distributed illuminance on a 1 square meter area.
Generally active luminous light-emitting intensity units candlelight CD, such as incandescent, LED, etc; reflected or penetrating-type objects luminous flux units lumens L, such as LCD projectors, etc; and the illumination unit lux Lux, generally used for photography and other fields . Three kinds of units of measurement are numerically equivalent, but from a different point of view needs to understand. For example: If an LCD projector brightness (luminous flux) of 1600 lumens, its projection to the total reflection of the screen size of 60 inches (1 square meter), its illumination of 1600 lux, assuming that the light exit from the light source 1 cm, the light exit area of one square centimeter, is the luminous intensity of light port is 1600CD. The real LCD projectors due to the light propagation loss, reflection or translucent membrane loss and light distribution uneven, brightness will be greatly reduced, generally 50% efficiency on the good.
Actual use, the light intensity calculation is often relatively easy to use mapping data units or change the use. For the LED display such initiatives emitters commonly used CD / square meter as the unit of luminous intensity, and with the observed angle of auxiliary parameters, which is equivalent to the surface of the screen illumination units lux; this value to the screen body effective display area multiplied by the best perspective on the entire screen of the luminous intensity, assuming screen luminous intensity of each pixel in the corresponding space constant, this value can be considered but also the entire screen body of luminous flux. General outdoor LED display is required to achieve 4000CD / square meter or more before the brightness of the sun under the ideal display. Common indoor LED, the maximum brightness in the 700 ~ 2000 CD / square meters.
Single LED luminous intensity in CD units:
With a perspective parameters, the luminous intensity and LED color does not matter. Single tube of luminous intensity from several mCD mCD five thousand dollars. Luminous intensity LED manufacturers are given the means at 20mA LED current is lit, the point of maximum intensity of light emission on the best perspective on the center position. LED package when the top of the lens shape and the position of the LED chip from the top of the lens determines the angle and LED light intensity distribution. Generally speaking the same LED larger perspective, the smaller the maximum luminous intensity, but the cumulative luminous flux in the entire three-dimensional hemisphere surface unchanged.
When a plurality of LED emission rules than the close, the superposition of luminous sphere, resulting in the emission plane luminous intensity is more evenly distributed. In calculating the luminous intensity of the display, to be based on LED perspective and LED emission density, the maximum point of luminous intensity value multiplied by the manufacturers to provide a 30% to 90%, and average luminous intensity as a single tube.
Manufacturers are generally marked as 100,000 hours or more, should also pay attention to the actual LED brightness decay cycle, such as most of the UR for automotive taillights lit red tube more than a dozen to a few hours later, the brightness is only half of the original. Brightness decay cycle and LED production process has a lot of material, generally in the case of economic conditions permit should choose brightness decay slower four-element LED.
Color, white balance:
White is by mixing red, green and blue brightness ratio is made when the green light to 69% brightness, 21% brightness of red, blue luminance of 10%, blending descendants eyes feel is pure white . But the chromaticity coordinates of red, green and blue LED due process and other reasons can not achieve all chromatographic results, control the colors, including a deviation of the brightness of colors are white light, called color.
When ago color full-color LED display, in order to achieve the best brightness and lowest cost, should try to choose the three primary colors luminous intensity into a roughly 3: 6: 1 ratio of LED devices composed of pixels.
White balance requires three primary colors in the same tone gray value of synthesis is still pure white.
Primary basic colors that can synthesize a variety of colors. Shade in the colors red, green, blue, next picture shows the spectrum table, table three vertices of an ideal primary color wavelength. If there are deviations colors, the color can be synthesized region will reduce spectral triangular table will be reduced, from the visual point of view, the color deviation will not only reduce the richness.
LED emits red, green, and blue light wavelengths according to their different characteristics and is broadly divided into purple, pure red, orange, orange, orange, yellow, green, pure green, green, blue, blue, blue-violet, orange , green, blue purple than pure red, pure green, Chunlan much cheaper prices. Three primary colors in the green of the most important, because green white occupied 69% brightness, and color at the center of a lateral row of the list. Therefore, when weighing the relationship between price and purity of color between green target is an important consideration.
Second, LED anti-static requirements
Blue, pure green, blue green, white, violet, purple light emitting diode belonging to an anti-static sensitive devices, handheld and packaging production process, please note take appropriate precautions, the following reference:
You must be able to prevent static electricity: assembling operation personnel should wear anti-static clothing (such as anti-static clothing, hats, shoes, gloves or finger cots, etc.)
We must be able to quickly surface or the interior of the dissipation of electrostatic: Assembly required the operator to wear anti-static wrist strap.
Provides shielding from electrostatic discharge or electric shock suddenly:
① assembly station (table) need to use anti-static mat and ground.
② LED costumes need to use anti-static component box.
③ iron, cutting-foot, tin stove (or automatic reflow equipment) are grounded.
Job, try to avoid directly touching the arc tube of the pin contact colloid take part when handling possible.
Measures should be completely grounded to prevent static electricity generation, table, iron, cutting-foot, tin stove (or automatic reflow equipment) of the ground must be introduced within the soil with a thick wire at the wire ,, not end tied big iron buried surface one meter below the ground line is required for each connected together with the main operator if wearing static ring of lead, lead will also need to turn on the buried line.
Semi-finished and finished products testing equipment should also be grounded.
Three, LED Caution
(1) characteristics of the LED diode approaching stability, voltage changes 0.1V, operating current may vary around 20mA. For safety, the use of a series current limiting resistor under ordinary circumstances, a great energy loss is obviously not suitable for solar lawn lights, and LED brightness varies with the operating voltage. The booster circuit is a good way, you can also use a simple constant current circuit, in short, must automatically limit, otherwise it will damage the LED.
(2) General LED peak current 50 ~ 100mA, reverse voltage at 6V, careful not to exceed this limit, in particular, reverse battery or load, the peak voltage is too high when the booster circuit is likely to exceed the limits of the solar cell, damage to the LED.
(3) LED temperature characteristic is not good, the temperature rise 5 ℃, flux decline of 3% in summer to use more attention.
(4) Operating voltage discrete large, same model, same batch of LED operating voltage has some differences, should not be used in parallel. If you must use in parallel, it should take full account of circumstances flow.
(5) Super bright white LED color temperature is 6400 ~ 30000k, the current low color temperature super bright white LED yet entered the market, so the penetration of solar lawn lights with super bright white LED manufactured relatively poor, this optical design on to attract attention.
(6) large electrostatic super bright white LED effects when you install should have anti-static facilities, workers have to wear an antistatic wrist strap to ESD damage was super bright white LED may not see with the eyes, but life It will become shorter.