LED light source and the traditional light source in the physical size and luminous flux, spectrum, light intensity of the spatial distribution and so there are very different, LED detection can not copy the traditional light source detection standards and methods. Let us below for you to introduce the common LED lighting detection technology.
Detection of Optical Parameters of LED Lamps
1, luminous intensity detection
Light intensity, ie, the intensity of light, refers to the amount of light emitted at a particular angle. CIE127 standard provides a measure of the light intensity of the measurement conditions A (far-field conditions), measurement conditions B (near-field conditions) two measurement average method is the most important method for the measurement of light intensity, To the light of the conditions, two conditions of the detector area are 1cm2. Normally, the luminous intensity is measured using standard condition B.
2, luminous flux and light efficiency detection
The luminous flux is the sum of the 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 lights and the measured lamps are sequentially ignited, and their readings in the photoelectric converter are recorded as Es and ED, respectively. When the standard luminous flux is known Φs, the luminous flux ΦD = ED × Φs / Es of the measured lamp. Integral method using the "point light source" principle, simple operation, but by the standard lamp and the measured lamp color temperature deviation, the measurement error.
(2) spectroscopy. The luminous flux is calculated from the spectral energy P (λ) distribution. The monochromator is used to measure the 380nm ~ 780nm spectrum of the standard lamp in the integrating sphere, and then the spectrum of the measured lamp is measured under the same conditions, and the luminous flux of the measured lamp is calculated and compared.
The luminous efficiency is the ratio of the luminous flux emitted by the light source to the power consumed by it, and the luminous efficiency of the LED is usually measured by constant current.
3, Spectral characteristics of detection
LED spectral characteristics of the detection, including spectral power distribution, color coordinates, color temperature, color rendering index and so on.
The spectral power distribution indicates that the light of the light source is composed of many different wavelengths of color radiation, and the radiated power of each wavelength is also different. This arrangement is called the spectral power distribution of the light source. The light source was measured by a spectrophotometer (monochromator) and a standard lamp.
The color coordinates are numerically represented by the amount of light emitted by the light source on the graph. There are a variety of coordinate systems that represent color, usually X, Y coordinate system.
Color temperature is the amount of light color table (appearance color performance) that the human eye sees. The light emitted by the light source is the same as the light color emitted by the absolute blackbody at a certain temperature, which is the color temperature. In the field of lighting, color temperature is an important parameter that describes the optical characteristics of the light source. The theory of color temperature is derived from blackbody radiation and can be obtained from the color coordinates of the blackbody trajectory by the color coordinates of the light source.
The color rendering index indicates that the light emitted by the light source is correctly reflected by the color of the illuminated object, usually expressed by the general color rendering index Ra, Ra is the arithmetic mean of the light color on the eight color rendering indices. Color rendering index is an important parameter of the quality of the light source. It determines the application range of the light source and improves the color rendering index of the white LED. It is one of the important tasks of LED research and development.
4, Light intensity distribution test
The relationship between the light intensity and the spatial angle (direction) is called the light intensity distribution, and the closed curve of this distribution is called the light intensity distribution curve. As the test points are more, and each point by the data processing, usually using an automatic distribution of photometer to measure.
5, The effect of temperature on the optical properties of LED
The temperature will affect the optical characteristics of the LED. A large number of experiments can show that the temperature affects the LED emission spectrum and color coordinates.
6, The surface brightness measurement
Light source in a certain direction of the brightness of the light source in the direction of the projection area of the luminous intensity, the general use of surface brightness meter, aiming brightness meter to measure the surface brightness, a light path and measuring light path 2 parts.
LED lamps and other performance parameters of the measurement
1, LED lighting electrical parameters of the measurement
Electrical parameters, including forward, reverse voltage and reverse current, related to the normal operation of LED lamps, LED lamps are to determine the basic performance of one of the basis. LED lamps have two kinds of electrical parameters measurement: the current is certain circumstances, the test voltage parameters; voltage must be the case, the test current parameters. The specific method is as follows:
(1) forward voltage. The positive current is applied to the LED lamp to be detected, and a voltage drop is generated at both ends. Adjust the current value to determine the power supply, record the DC voltmeter on the relevant readings, that is, LED lamps forward voltage. According to the relevant common sense, LED positive conduction, the resistance is small, the use of ammeter external method more accurate.
(2) reverse current. To the detection of LED lamps to apply reverse voltage, adjust the power supply, ammeter reading is the measured LED lamp reverse current. And measure the positive voltage with the same reason, because the LED reverse conduction resistance when the larger, using ammeter internal connection.
2, LED lamp thermal properties test
LED thermal properties, the LED optical properties, electrical characteristics have an important impact. Thermal resistance and junction temperature, is the main thermal properties of LED2. Thermal resistance refers to the thermal resistance between the PN junction and the surface of the shell, ie 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.
Measuring LED junction temperature and thermal resistance methods are: infrared micro-instrument method, spectroscopy, electrical parameters, thermal resistance scanning method. Using infrared thermometer or micro-thermocouple measured LED chip surface temperature as LED junction temperature, accuracy is not enough.
At present, the commonly used electrical parameter method is the linear relationship between the forward voltage drop of the LEDPN junction and the PN junction temperature. The junction temperature of the LED is measured by measuring the forward voltage drop at different temperatures.