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8 common LED lighting detection technology
- Jan 05, 2018 -

8 common LED lighting detection technology

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LED light source and the traditional light source in the physical size and luminous flux, spectral, spatial distribution of light intensity and so there is a big difference, LED detection can not copy the traditional light source detection standards and methods. Xiaobian introduce you to the following common LED lighting detection technology.


LED lighting optical parameters of the test


1, luminous intensity detection


Light intensity is the intensity of light, refers to the amount of light emitted in a particular angle. Due to the concentration of LED light, the inverse square inverse law is not applicable at close range. The CIE127 standard provides two measurement averaging methods for measuring light intensity A (far-field conditions) and measuring conditions B (near-field conditions) To the light conditions, the two conditions of the detector area are 1cm2. Normally, the standard condition B is used to measure the luminous intensity.


2, luminous flux and light efficiency testing


Luminous flux is the total amount of light emitted by the light source, that is, the amount of light. Detection methods include the following two kinds:


(1) integral method. In the integrating sphere, the standard lamp and the lamp under test are sequentially lit, and their readings on the photoelectric converter are respectively Es and ED. The standard lamp flux is known Φs, the luminous flux of the lamp under test ΦD = ED × Φs / Es. Integral method using "point light" principle, simple operation, but by the standard lamp and the lamp under the influence of color temperature deviation, measurement error greater.


(2) spectrophotometry. The luminous flux is calculated from the spectral energy P (λ) distribution. Using a monochromator, measure the 380 nm ~ 780 nm spectrum of the standard lamp in the integrating sphere, measure the spectrum of the lamp under the same conditions, and compare the luminous flux of the lamp under test.


Luminous efficiency is the ratio of the luminous flux emitted by a light source to the power consumed by it, and the luminous efficacy of the LED is usually measured by a constant current method.


3, the spectral characteristics of testing


The spectral characteristics of LED detection, including spectral power distribution, color coordinates, color temperature, color rendering index and so on.


The spectral power distribution means that the light of a light source is composed of a plurality of color radiations of different wavelengths, and the radiant power of each wavelength is also different in size. This difference is called the spectral power distribution of a light source in order of wavelength. The use of spectrophotometer (monochromator) and standard light source for comparison and measurement.


Color coordinates are digitally represented on the graph the amount of light emitted by a light source. There are many coordinate systems for color coordinates, usually X, Y coordinate system.


Color temperature is the amount of light color table (appearance color performance) that the human eye sees. When the light emitted by the light source is the same color as the light emitted by the absolute black body at a certain temperature, the temperature is the color temperature. In the field of lighting, color temperature is an important parameter to describe the optical characteristics of a light source. The theory of color temperature stems from blackbody radiation and can be obtained from the color coordinates of a blackbody locus through the color coordinates of the light source.


The color rendering index indicates that the amount of light emitted by the light source correctly reflects the color of the illuminated article, usually expressed as the general color rendering index Ra, which is the arithmetic mean of the color rendering indices of the eight color samples by the light source. Color rendering index is an important parameter of light source quality, which determines the application of light source, improve the color rendering index of white LED is one of the important tasks of LED research and development.


4, light intensity distribution test


Light intensity with the spatial angle (direction) and the relationship between the said pseudo-light intensity distribution, by the distribution of the closed curve is called the light intensity distribution curve. Due to the large number of measurement points and the data processing at each point, an automatic photometer is usually used for the measurement.


5, the temperature effect on the optical characteristics of LED


The temperature will affect the optical properties of the LED. A large number of experiments can explain the temperature of the LED emission spectrum and color coordinates.


6, the surface brightness measurement


The brightness of a light source in one direction is the luminous intensity of the light source in the projection area of the unit in this direction. Generally, the surface brightness meter and the aiming brightness meter are used to measure the surface brightness, and the aiming light path and the measuring light path are two parts.


LED lamps and other performance parameters of the measurement


1, LED lamps electrical parameters of the measurement


Electrical parameters include forward, reverse voltage and reverse current, LED lamps related to the normal work, is to determine the merits of the basic performance of LED lamps one of the merits. LED lamps have two kinds of electrical parameters of measurement: the current under certain circumstances, the test voltage parameters; voltage under certain circumstances, the test current parameters. Specific methods are as follows:


(1) forward voltage. A positive current is applied to the LED lamp to be tested, with a voltage drop across it. Adjust the current value to determine the power supply, record the relevant readings on the DC voltmeter, which is the forward voltage of LED lamps. According to common sense, LED forward conduction, the smaller resistance, the use of ammeter external connection method more accurate.


(2) reverse current. To be tested by the reverse voltage LED lighting, regulating power supply, ammeter reading is measured LED lamps reverse current. And the same measurement of forward voltage, because the LED reverse conduction larger resistance, the use of ammeter connection method.


2, LED lamps thermal characteristics of the test


Thermal characteristics of LED, LED optical properties, electrical properties have a significant impact. Thermal resistance and junction temperature, LED2 is the main thermal characteristics. Thermal resistance refers to the thermal resistance between the PN junction and the surface of the housing, that is, the ratio of the temperature difference along the heat flow path to the power dissipated on the channel. The junction temperature is the temperature of the PN junction of the LED.


Methods of measuring LED junction temperature and thermal resistance are generally: infrared microscopy method, spectroscopy, electrical parameter method, thermal resistance scanning method. The use of infrared temperature microscope or miniature thermocouple measured LED chip surface temperature as LED junction temperature, accuracy is not enough.


The commonly used method of electrical parameters is the use of LEDPN junction forward voltage drop and PN junction temperature into a linear relationship between the characteristics of different temperatures by measuring the forward voltage drop LED junction temperature obtained.




Source: China LED Network