The factors that affect the light color and light-emitting efficiency of LED are the materials and manufacturing process of LED, red, green and blue are widely used currently. Because the working voltage LED is low (only 1.5-3V), it can emit light spontaneously and has certain brightness, and the brightness can be adjusted by voltage (or current), and it also features impact-resistant, anti-vibration, long lifespan (100,000 hours). Different manufacturing materials of LED can generate photons with different energies in order to control the wavelength of light emitted from LED, which means spectrum or color.
the material used to manufacture the first LED in the history is arsenic (As) of gallium (Ga), its PN junction forward voltage drop (VF, can be understood as lighting or working voltage) is 1.424V, and the light it emitted was infrared spectrum. Another commonly used material for LED is phosphorus (P) of gallium (Ga), its PN junction forward voltage drop is 2.261V, and the light it emits is green light.
Based on these two kinds of materials, the early LED industry used GaAs1-xPx material structure, which in theory can produce LEDs with any wavelength within the range from the infrared light to green light, subscript X stands for the percentage of phosphorus to replace arsenic. Generally LED's wavelength and color can be determined through the PN junction voltage drop. There are some typical LEDs such as GaAs0.6P0.4 red LED, GaAs0.35P0.65 orange LED, GaAs0.14P0.86 yellow LED and so on. Since the three elements of gallium, arsenic and phosphorus are used to manufacture these LEDs, they are commonly referred to as three-element light emitting tube.
And GaN (gallium nitride) blue LED, GaP green LED and GaAs infrared LED are commonly referred to as two-element light emitting tube. The latest manufaturing process utilizes four-element LEDs with four-element material which mixes aluminum (Al), calcium (Ca), indium (In) and nitrogen (N), which can contain the spectrum range of all visible light and some ultraviolet light.
Luminous intensity: there are three light intensity measurement units, unit of illuminance (Lux), luminous flux unit (Lumen) and luminous intensity unit (Candle power) 1CD (candlelight) means under the freezing point temperature of platinum, the total radiation objects' luminous intensity of every sixtieth square centimeter area. (also means the luminous intensity of a diameter 2.2 cm, 75.5 gram whale oil candle which is burning 7.78 grams per hour with a flame height of 4.5cm along the horizontal direction). 1L (lumen) means the luminous flux of 1 CD candle light lighting in the distance of 1 cm on a 1 square centimeter plane.
1Lux means the illuminance generates when 1L of luminous flux evenly distributed on the area of 1 square meter. Generally active luminophor use luminous intensity unit CD, such as incandescents, LEDs and so on; reflection or transmission type of objects use Luminous flux unit Lumen, such as LCD projector and so on; and illumination unit Lux is generally used in photography and other fields. Three types of measurement units are equivalent in value, but we need to understand from different perspectives. For example: If an LCD projector brightness (luminous flux) is 1600 lumens, the projecting size to the total reflection screen is 60 inches (1 square meter), and its illuminance is 1600 lux, we assume the distance from light source to the light exit is 1 cm, the light exit area is 1 square centimeter, and the light intensity of the light exit is 1600CD. But as a matter of fact LCD projectors' brightness will be adversely affected because of the loss of light transmission, reflection or translucent film loss and uneven distribution of light, 50% efficiency is a normal or good result.
In actual use, the light intensity calculation often utilizes the unit which is easy to measure. for the active luminophor LED display we generally use CD/square meter as the unit of luminous intensity with the observing angle as auxiliary parameters, which is equivalent to the illumination unit lux of the screen surface; multipling this value with the effective display area of the screen will generate the luminous intensity of the whole screen in the visual angle, Suppose luminous intensity of each pixel in the corresponding space of the screen body is constant, and this value can be considered as the luminous flux of the whole screen. Only when common outdoor LED screens achieve a brightness of 4000CD/square meter or more should they have ideal display effect under the sun. The maximum brightness of common indoor LED is around 700 ~ 2000 CD/square meter.
Single LED luminous intensity use CD as unit with visual angle parameters, LED luminous intensity has nothing to do with LED color. Luminous intensity of Single LED varies from several mCD to 5000mCD. Luminous intensity given by LED manufacturers means the point in the best visual angle and in the center position with the maximum LED luminous intensity when the LED is lit up under 20mA current. The shape of the lens on the top and the distance between the top lens and LED chips determines the beam angle and light intensity distribution of LEDs when packaging LEDs. Generally speaking, for the same LED, the bigger the beam angle is, the smaller the maximum luminous intensity is, but the accumulated luminous flux on the surface of the whole three-dimensional hemisphere is constant. When the several LEDs are arrayed closely and regularly, their lighting spheres will overlap, which will result in even luminous intensity distribution on the whole light-emitting surface.
When calculate the luminous intensity of the screen, the luminous intensity value of the maximum point shall be multiplied by 30% to 90% accroding to the visual angle of LEDs and array density of LEDs, which can be considered as the average light intensity of single LED. Generally LEDs have a long lifespan, and manufacturers always mark that the lifesapn is more than 100,000 hours, actually we should also pay attention to LED brightness degradation cycle, such as majority of the UR LEDs for automotive taillights have only the half brightness as before after lighting for dozens of hours.
The manufacturing process of LED material affect LED brightness degradation cycle a lot, if economic condition permits we should select four-element LEDs with a slow brightness degradation cycle. White is a mixed color of red, green and blue according to the brightness proportion, When the brightness of green in the light is 69%, the brightness of red is 21%, the brightness of blue is 10%, the human eyes feel pure white after mixing the colors. But the color coordinate of the red, green and blue LEDs unable to achieve the effects of full chromatograms because of manufacturing process and other reasons, and controlling the brightness of primary colors including biased primary colors to generate white light is called matching colors. Before matching colors for the full-color LED display screen, in order to achieve the best brightness and lowest cost, we should choose the LEDs whose luminous intensity proportion of the three primary colors is around 3:6:1 to compose pixels.
White balance requires that the color mixed by three primary colors under the same gray adjustment value is still pure white. Primary colors, fundamental colors: the basic colors that can synthesize a variety of colors. The primary colors in the color light are red, green and blue.
The red, green and blue light that LED emits, according to their different wavelengths characteristics, can be sorted into purple red, pure red, orange red, orange, orange yellow, yellow, yellow green, pure green, jade green, blue green, pure blue, blue purple and so on, orange red, yellow green and blue purple are much cheaperthan pure red, pure green and pure blue. Green is the most important among the three primary colors, because green accounts for 69% of the brightness in the white color, and it locates at the center of the color horizontal array. Therefore, we should balance the purity and price of the color to determine the composition methods of the three primary colors, in three-color design applications we usually achieve the white balance and maximum expected brightness value by adjusting and setting the LED current.