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The Nine Parameters to Evaluate LED

Data: 2016-08-12

           The Nine Parameters to Evaluate LED

    1. The Current/Voltage(Forward or Reverse) Parameter of LED
LED has a typical volt-ampere characteristic of P-N junction. The current in the LED directly affects its luminous intensity. Each relevant property of LED must match the characteristic and its characteristic of reverse current must be considered in the condition of communication. Therefore, their forward current and voltage drop must be tested as they are working, and parameters such as reverse leakage current and reverse breakdown voltage.
    2. The Luminous and Radiation Flux of LED
The launch of the total electromagnetic energy in LED per unit time is called Radiation Flux, namely Light Power (W). As for LED light source, the visual effect of lighting in paid more attention, that is, the radiation flux of light source emisssion can cause people to feel the quantity of eye perception, called Luminous Flux. The ratio of the radiation flux and the electric power of devices named the LED's Radiation Efficiency.
     3. The Luminous Intensity Distribution Curve of LED
The luminous intensity distribution curve is used to represent the space distribution of LED light in diifenrent directions. In lighting applications, the intensity distribution is the most basic data while calculating working face illumination uniformity and LED the space layout. When spatial beam of LED represents ratational symmetry distribution, a  plane of the beam axis can be used. To beam for elliptic distribution of LED, the beam axis and the curve of two vertical planes in major and minor axis of ellipse are used to represent. To asymmetric complex graphics, the beam axis over six sections of plane curve is used to represent.
     4. The Spectral Power Distribution of LED
The spectral power distribution of LED represents the function of  radiation power with the wavelength change. It determines the luminous color and its luminous flux, color rendering index. Usually, the relative spectral power distribution is expressed as the letter, S(λ). When the spectral power fall to 50% of its value along the both sides of its peak value, the corresponding difference(Δλ=λ2-λ1) between the two wavelengths is the spectral band.
     5. The Chromaticity Coordinate of LED
For the three primary colors red (R), green (G), blue (B), x = R/(R + G + B), y = G/(R + G + B), z = (R + G + B). Due to x + y + z = 1, just give the value of x and y, and  a certain color can be ascertained, which is usually called a chromaticity diagram. With x, y forming the plane-coordinate system, using colorimetric experimental method to measure the value of x, y of colors in nature, and darwing them in the plane coordinate, a chromaticity diagram can be got. Any point along the tongue curve in the diagram represents the color of a certain wavelength, while any point inside the diagram indicates a certain mix of light color people can see. Among them, the color temperature of the feature points A, B, C, D, E of the area in the color coordinate can be seen in the following table.

      6. The Color Temperature and Color Rendering Index
For the LED illuminant, its apparent color can be accurately expressed by color coordinate, but the specific value is difficult to associate with the conventional light color. People often regard light color with slight orange as "warm color", and dazzling white or slight blue as "cool color". Thus, using color temperature to represent the color of light source will be more intuitive.
      7. The Thermal Performance of LED
To improve LED luminous efficiency and power is one of the key problems in the current LED industry development. At the same time, the problem about the temperature of PN junction and the heat dissipation is particularly important, generally  expressed by parameters such as thermal resistance, shell and junction temperature.
       8. The Radiation Safety of LED
At present, the international electrotechnical commission (IEC) will make a radiation safety test and demonstration on LED products according to the requirements of the semiconductor lasers. Considering the possiblity of its harmful  radiation to human eyes' retina, as a light-emitting device with narrow beam of light and high brightness, LED is stipulated its radiation limit requirements and testing method for different occasions application by the international standard. Nowadays, the radiation safety of LED lighting products is implenmented as a  mandatory safety requirement in the European Union and the United States.
       9. The Reliability and Lifespan of LED
Reliability index is used to measure LED's ability to work in different environments; lifespan is the quality index to evaluate available cycle of LED products, usually expressed in effective life or ending life. In lighting applications, effective life means the lasting time that  LED luminous flux attenuates to the percentage of the initial value (stipulated number) under the condition of rated power.
       (1). The average life expectancy refers to the spent time when a batch of LED lights at the same time, the proportion of not lighting LED reaches 50%  after a period of time.
       (2). The economic life refers to the time that LED's comprehensive light output attenuates to a certain pertentage, considering the conndition of LED damage and attenuation of light output. For outdoor lighting the proportion is at 70% , for indoor lighting at 80%.

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