How to test the performance of machine vision light source

How to test the performance of machine vision light source

Jan 05 2021

   How can I test the performance of the machine vision light source I buy? Is it that every brand of the same type of light source is the same? The answer is of course not the same, the detection of machine vision light source performance can be observed from several points, the following machine vision to follow the Waldrop to detect the performance of machine vision light source good or bad!
 
  1. Luminous intensity detection 
 
    Light intensity is the intensity of light, refers to the amount of light radiated within a particular angle. Because the LED light is more concentrated, in the case of close range does not apply to the inverse square law, CIE127 standard for the measurement of light intensity proposed measurement conditions A (far-field conditions), measurement conditions B (near-field conditions) two conditions for measuring the average normal light intensity, the detector area of the two conditions are 1cm2. usually, the use of standard conditions B measurement of luminous intensity.
 
  2. Luminous flux and luminous efficiency detection 
 
    Luminous flux is the sum of the amount of light emitted by the light source, that is, the amount of luminescence. Detection methods mainly include the following 2 kinds.
 
 (1) integration method. The standard light flux is known Φs, the luminous flux of the measured lamp ΦD = ED × Φs/Es. The integration method uses the "point source" principle, simple operation, but the standard lamp and the measured lamp color temperature deviation, the measurement error is larger. The measurement error is large.
 
 (2) Spectroscopic method. The luminous flux is calculated by the spectral energy P (λ) distribution. Using a monochromator, the 380nm to 780nm spectrum of the standard lamp is measured in the integrating sphere, and then the spectrum of the lamp under test is measured under the same conditions, and the luminous flux of the lamp under test is calculated by comparison.
 
    Luminous efficacy is the ratio of the luminous flux emitted by the light source to the power it consumes, and the luminous efficacy of LEDs is usually measured in a constant-current manner.
 
  3. Spectral characteristics detection 
 
    LED spectral characteristics testing includes spectral power distribution, color coordinates, color temperature, color rendering index and other content.
 
    Spectral power distribution indicates that the light of the light source is composed of many different wavelengths of color radiation, the size of the radiation power of each wavelength is also different, this difference with the wavelength order is called the spectral power distribution of the light source. The use of spectrophotometer (monochromator) and the standard lamp for the light source to compare the measurement to obtain.
 
    Color coordinates are digitally represented on a coordinate chart of the light source's luminescent color quantity. There are a variety of coordinate systems that represent the color coordinate chart, usually using the X and Y coordinate system.
 
    Color temperature is the amount of light source color table (appearance of color performance) as seen by the human eye. When the light emitted by a light source is the same color as the light emitted by an absolute blackbody at a certain temperature, that temperature is the color temperature. In the field of lighting, color temperature is an important parameter in describing the optical properties of a light source. The theory related to color temperature originates from blackbody radiation and can be obtained from the color coordinates of a light source containing a blackbody trajectory.
 
    The color rendering index indicates the amount of light emitted by a light source that correctly reflects the color of the illuminated object, and is usually expressed by the general color rendering index Ra, which is the arithmetic mean of the color rendering index of the light source for eight color samples. Color rendering index is an important parameter of the quality of the light source, it determines the application range of the 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 is called false light intensity distribution, the distribution of this kind of closed curve is called light intensity distribution curve. Due to the number of measurement points, and each point is processed by the data, usually using automatic distribution photometer for measurement.
 
  5. Temperature effect on the optical properties of LEDs 
 
    Temperature affects the optical properties of LEDs. A large number of experiments can show that the temperature affects the LED emission spectrum and color coordinates.
 
  6. Surface brightness measurement 
 
    The luminance of the light source in a certain direction is the luminous intensity of the light source in the direction of the unit projection area, the general use of surface luminance meter, aiming type luminance meter to measure the surface luminance, there are 2 parts of the aiming light path and measuring light path.
 
  7.LED lamps and lanterns electrical parameters measurement 
 
    Electrical parameters mainly include forward, reverse voltage and reverse current, related to the LED lamps and lanterns can work properly, is one of the basis for determining the basic performance of LED lamps and lanterns. 2 kinds of electrical parameters measurement of LED lamps and lanterns: that is, the case of a certain current, test the voltage parameters; voltage a certain case, test the current parameters. Specific methods are as follows.
 
 A. Forward voltage. Apply a forward current to the LED lamp to be tested, which will produce a voltage drop across its terminals. Adjust the current value to determine the power supply, record the relevant readings on the DC voltmeter, that is, the forward voltage of the LED lamps. According to the relevant common sense, LED forward current, the resistance is small, the use of ammeter external method is more accurate.
 
 B. Reverse current. Apply reverse voltage to the tested LED luminaire, adjust the voltage regulator, the ammeter reading is the reverse current of the tested LED luminaire. The same as measuring the forward voltage, because the LED reverse conduction resistance is larger, using the ammeter internal connection method.
 
  8. LED lamps and lanterns thermal characteristics test 
 
    LED thermal characteristics, the optical characteristics of the LED, electrical characteristics have an important impact. Thermal resistance and junction temperature, is the 2 main thermal characteristics of LED. Thermal resistance is the thermal resistance between the PN junction and the surface of the housing, that is, the temperature difference along the heat flow channel and the ratio of the power dissipated on the channel, junction temperature is the temperature of the PN junction of the LED.
 
    The methods of measuring LED junction temperature and thermal resistance are generally: infrared micro-imaging method, spectroscopic method, electrical parameter method, optical thermal resistance scanning method, etc. Using infrared temperature microscope or micro thermocouple to measure the surface temperature of the LED chip as the junction temperature of the LED, the accuracy is not enough.
 
    At present, the commonly used electrical parameter method is to use the property that the forward voltage drop of the LED PN junction is linearly related to the PN junction temperature, and the junction temperature of LED is obtained by measuring the forward voltage drop difference at different temperatures.