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# 8 characteristic parameters of white LED

May 23, 2019

1. Current/voltage parameters of white LEDs (positive and reverse)

The white LED has a typical PN junction volt-ampere characteristic. The current directly affects the luminance of the white LED and the PN string parallel connection. The characteristics of the relevant white LEDs must be matched. In the AC mode, the reverse must also be considered. Electric characteristics. Therefore, they must be tested for forward current and forward voltage drop at the operating point, as well as parameters such as reverse leakage current and reverse breakdown voltage.

2. Luminous flux and radiant flux of white LED

The total electromagnetic energy emitted by a white LED in a unit of time is called the radiant flux, which is the optical power (W). For the white LED light source for illumination, the more concerned is the visual effect of illumination, that is, the amount of radiant flux emitted by the light source that can cause the human eye to perceive, called the luminous flux. The ratio of the radiant flux to the electrical power of the device represents the radiation efficiency of the white LED.

3. Light intensity distribution curve of white LED

The light intensity distribution curve is used to indicate the distribution of the light emitted by the LED in all directions of the space. In lighting applications, the light intensity distribution is the most basic data when calculating the illuminance uniformity of the working surface and the spatial arrangement of the LEDs. For a LED whose spatial beam is rotationally symmetric, it can be represented by a curve of the plane of the beam axis; for an LED with an elliptical beam, the curve of the two vertical planes of the beam axis and the elliptical axis are used. To represent an asymmetrical complex figure, it is generally represented by a plane curve of more than 6 sections of the beam axis.

4, the spectral power distribution of white LED

The spectral power distribution of a white LED represents a function of the radiant power as a function of wavelength. It determines both the color of the luminescence and its luminous flux and color rendering index. Generally, the relative spectral power distribution is represented by the text S(λ). When the spectral power drops to 50% of its value along both sides of the peak, the difference between the two wavelengths (Δλ=λ2-λ1) is the spectral band.

5, color temperature and color rendering index of white LED

For a light source such as a white LED that emits substantially white light, the chromaticity coordinates can accurately express the apparent color of the light source, but the specific value is difficult to associate with the customary light color perception. People often refer to the light-colored orange-red color as "warm color", and the more blazing or slightly blue-colored ones are called "cold color". Therefore, it is more intuitive to use color temperature to indicate the light color of the light source.

7, the thermal performance of white LED

The improvement of LED luminous efficiency and power for lighting is one of the key issues in the current development of the LED industry. At the same time, the PN junction temperature of the LED and the heat dissipation problem of the housing are particularly important, and are generally expressed by parameters such as thermal resistance, case temperature, and junction temperature.

8, radiation safety of white LED

At present, the International Electrotechnical Commission (IEC) equates LED products with the requirements of semiconductor lasers for radiation safety testing and demonstration. Because LED is a narrow beam, high-brightness light-emitting device, considering its radiation may be harmful to the human eye retina, the international standard specifies the limits and test methods for effective radiation for LEDs used in different occasions. Radiation safety for lighting LED products is currently implemented as a mandatory safety requirement in the European Union and the United States.

9, the reliability and life of white LED

Reliability metrics are used to measure the ability of LEDs to function properly in a variety of environments. Lifetime is a measure of the useful life of an LED product and is usually expressed in terms of useful life or end-of-life. In lighting applications, the effective life is the time it takes for the LED to decay to the percentage of the initial value (prescribed value) at rated power.

(1) Average life: The time taken for a batch of LEDs to illuminate at the same time, when the proportion of non-bright LEDs reaches 50% after a period of time.

(2) Economic life: When considering both LED damage and attenuation of light output, the integrated output is reduced to a certain proportion of time, which is 70% for outdoor light sources and 80% for indoor light sources.