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Faq

8 common LED lighting inspection technology

Time:2017-05-22 Views:338
  LED light source and the traditional light source in the physical size and luminous flux, spectral and spatial distribution of light intensity had significant difference, the LED test cannot copy detection standards and methods of traditional light source. Here is a look at the detection technology of common LED lamps.
  
  Detection of LED lamp optical parameters
  
  Light intensity detection
  
  The intensity of light, the intensity of light, is the amount of light emitted at a particular Angle. Because of the LED light is relatively concentrated, in close cases shall not apply to the inverse square law, CIE127 standard put forward the measurement conditions of strong light (the far field condition), measuring condition B (near-field conditions) two measuring average method to the light intensity conditions, two conditions of detector area 1 cm2. Normally, the luminescence intensity is measured using standard B.
  
  Light flux and light detection
  
  Flux is the amount of light emitted by the light source. The detection methods mainly include the following two types:
  
  (1) the integral method. The standard lights are lit in sequence and the lamps are measured in order to record their readings of Es and ED respectively in the photoelectric converter. Φ s standard light flux is known, then tested the lamp luminous flux Φ D = ED x Φ s/Es. The integral method USES the principle of "point source", which is simple to operate, but the measurement error is large by the effect of the color temperature deviation of the standard lamp and the measured lamp.
  
  (2) spectra. The flux is calculated through the spectral energy P (lambda) distribution. Using monochromator, the standard lamp in the integrating sphere 380 nm to 780 nm spectral measurements, and then to be measured in the same condition to measure the spectrum of light, and contrast to calculate the measured light flux.
  
  The light effect of the light effect is the ratio of the flux to the power used, and the light effect of the LED is usually measured by a constant current method.
  
  Spectral characteristic detection
  
  The spectral characteristics of leds include spectral power distribution, color coordinates, color temperature, and color indices.
  
  Said spectral power distribution of the light source light is composed of many different color wavelengths of radiation, the wavelength of the radiation power of different sizes and this order is different with the wavelength is referred to as the light source spectral power distribution. Using spectrophotometer (monochromator) and standard lamp, the light source is compared to the measurement.
  
  The color coordinates represent the amount of luminescent color of the light source on the graph. There are multiple coordinates for the color scheme, usually in terms of X and Y coordinates.
  
  Color temperature is the amount of light color table (appearance color) that the human eye sees. The light emitted by the light source is the same as the light emitted by an absolute black body at a certain temperature, which is the color temperature. In lighting, color temperature is an important parameter describing the optical properties of light sources. The theory of color temperature is derived from black body radiation, which can be obtained through the color coordinates of the light source from the colored coordinates containing the black body locus.
  
  Color rendering index showed that light emission of light correctly reflect the amount of the color to be as content, usually expressed in general color rendering index Ra, the Ra is a source of eight color sample color rendering index arithmetic mean. The color index is the important parameter of the quality of the light source, it determines the application scope of the light source, and the color index of white leds is one of the important tasks of LED development.
  
  Light intensity distribution test
  
  The intensity of light varies according to the spatial Angle (direction), and the closed curve of this distribution is called the light intensity distribution curve. Because the measurement is more, and each point is processed by data, automatic distribution photometer is usually measured.
  
  The effect of temperature effect on LED optical properties
  
  Temperature affects the optical properties of leds. A large number of experiments show that the temperature influences LED emission spectra and color coordinates.
  
  Surface brightness measurement
  
  The brightness of the light source in a certain direction for the light source in the direction of the unit on the projection area of luminous intensity, the use of surface luminance meter, general target type meter measuring surface brightness, have aimed at light path and the measuring optical path of two parts.
  
  The measurement of other performance parameters of LED lamps
  
  Measurement of electrical parameters of LED lamps and lanterns
  
  Electrical parameter mainly includes the forward and reverse voltage and current, is related to the LED lamps and lanterns can work normally, one is the basis for determining basic performance of LED lamps and lanterns. The electrical parameters of LED lamps are measured in two kinds: if the current is certain, test voltage parameters. When the voltage is certain, the current parameter is tested. Here‘s how:
  
  (1) the forward voltage. To apply positive current to the LED lamp to be tested, voltage drop will occur at both ends. Adjust the power supply of the current meter, and record the relevant reading on the dc voltmeter, which is the positive voltage of LED lamps. According to relevant common sense, the resistance is small when the LED is in the guide, and it is more accurate to use the external method of the ammeter.
  
  (2) the reverse current. To apply reverse voltage to the LED lamps that are detected, adjust the voltage stabilizer, the reading of the current meter is the reverse current of the LED lamps. This is the same as measuring the forward voltage, because the LED anti-guide is more resistant to the current, and the current method is applied in the current meter.
  
  2, LED lamps heat learning characteristic test
  
  The thermal properties of LED are important to the optical properties and electrical properties of leds. Thermal resistance and junction temperature are the main heat properties of the LED2. Thermal resistance refers to the heat resistance between PN junction and the surface of the shell, which is the ratio of the temperature difference between the temperature difference on the heat flow path and the power dissipated on the channel, the temperature of the PN junction of the LED.
  
  The methods of measuring LED junction temperature and thermal resistance are generally: infrared microimaging, spectrophotometry, electrochemical parameter, photoresist, and so on. The surface temperature of LED chip with infrared temperature microscope or micro-thermocouple is not enough.
  
  Electrical parameters of the currently widely used method is to use LEDPN knot of positive pressure drop and the characteristics of a linear relationship with PN junction temperature under different temperature by measuring the pressure drop is poor to get the LED junction temperature.