Top 8 common LED lamp detection technologies

Eight common LED lamp detection technologies

there are great differences between LED light source and traditional light source in physical size, luminous flux, spectrum, spatial distribution of light intensity and so on. Led detection cannot copy the detection standards and methods of traditional light source. The following introduces the detection technology of common LED lamps

detection of optical parameters of LED lamps

1. Detection of luminous intensity

light intensity is the intensity of light, which refers to the amount of light emitted at a specific angle. Because the light of LED is relatively concentrated, the inverse square law does not apply in the case of short distance. Cie127 standard stipulates that there are two kinds of measurement conditions for the measurement of light intensity: measurement condition a (far-field condition) and measurement condition B (near-field condition). The average requirements for plastic are mainly two points: the condition of normal light intensity, and the detector area of both conditions is 1cm2. In general, the luminous intensity is measured using standard condition B

2. Luminous flux and luminous effect detection

luminous flux is the sum of the amount of light emitted by the light source, that is, the luminous amount. The detection methods mainly include the following two kinds:

(1) integral method. Ignite the standard lamp and the tested lamp in turn in the integrating sphere, and record their readings in the photoelectric converter as es and ED respectively. The luminous flux of standard lamp is known Φ s. Then the luminous flux of the tested lamp Φ D = e, which will also provide inexhaustible development impetus for the extruder industry D ×Φ s/Es。 The integral method uses the principle of "point light source", which is simple to operate, but the measurement error is large due to the color temperature deviation between the standard lamp and the tested lamp

(2) spectrophotometry. Through spectral energy p（ λ） The luminous flux is calculated from the distribution. Use a monochromator to measure the 380nm-780nm spectrum of the standard lamp in the integrating sphere, and then measure the spectrum of the tested lamp under the same conditions, and compare and calculate the luminous flux of the tested lamp

luminous efficiency refers to the ratio of luminous flux emitted by the light source to its consumed power. The luminous efficiency of LED is usually measured by constant current method

3. Spectral characteristic detection

led spectral characteristic detection includes spectral power distribution, color coordinates, color temperature, color rendering index, etc

spectral power distribution indicates that the light of the light source is composed of colored radiation of many different wavelengths, and the radiation power of each wavelength is also different. This difference is called the spectral power distribution of the light source in the order of wavelengths. Use spectrophotometer (monochromator) and standard lamp to compare and measure the light source

color coordinate refers to the amount of luminous color of light source on the coordinate diagram in a digital way. There are many coordinate systems in the coordinate diagram of color, usually X and Y coordinate systems

color temperature is the amount of light source color table (appearance color performance) seen by human eyes. When the light emitted by the light source is the same color as the light emitted by the absolute blackbody 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 light sources. The relevant theory of color temperature comes from blackbody radiation, which can be obtained from the color coordinates containing blackbody trajectories through the color coordinates of the light source

the color rendering index indicates the amount that the light emitted by the light source correctly reflects the color of the illuminated object. It is usually expressed by the general color rendering index RA, which is the arithmetic mean of the color rendering indexes of the light source for 8 color samples. Color rendering index is an important parameter of light source quality, which determines the application range of light source. Improving the color rendering index of white LED is one of the important tasks of LED research and development

4. Light intensity distribution test

the relationship between light intensity and spatial angle (direction) is called false b0.71 light intensity distribution, and the closed curve formed by this distribution is called light intensity distribution curve. Due to the large number of measuring points and the data processing of each point, it has played an important role in stabilizing China's industrial growth and accelerating the transformation and upgrading of manufacturing industry. Automatic distribution photometer is usually used for measurement

5. Influence of temperature effect on the optical properties of LED

temperature will affect the optical properties of LED. A large number of experiments can show that temperature affects the emission spectrum and color coordinates of LED

6. Surface brightness measurement

the brightness of the light source in a certain direction is the luminous intensity of the light source in the unit projected area in that direction. Generally, the surface brightness meter and aiming type brightness meter are used to measure the surface brightness. There are two parts: aiming light path and measuring light path

measurement of other performance parameters of LED lamps

1. Measurement of electrical parameters of LED lamps

electrical parameters mainly include forward and reverse voltage and reverse current, which are related to whether LED lamps can work normally and are one of the basis for judging the basic performance of LED lamps. There are two kinds of electrical parameters measurement of LED lamps: when the current is certain, test the voltage parameters; When the voltage is constant, test the current parameters. The specific methods are as follows:

(1) forward voltage. Apply a forward current to the LED lamp to be detected, and voltage drop will be generated at both ends. Adjust the power supply determined by the current value, and record the relevant readings on the DC voltmeter, which is the forward voltage of the LED lamps. According to relevant common sense, when the LED is conducting in the forward direction, the resistance is small, and the external connection method of ammeter is more accurate

(2) reverse current. Apply a reverse voltage to the tested LED lamp and adjust the regulated power supply. The reading of the ammeter is the reverse current of the tested LED lamp. It is the same as measuring the forward voltage, because the resistance of LED is large when it is turned on in reverse, so the internal connection method of ammeter is adopted

2. Thermal characteristics test of LED lamps

the thermal characteristics of LED have an important impact on the optical and electrical characteristics of LED. Thermal resistance and junction temperature are the main thermal characteristics of LED2. Thermal resistance refers to the thermal resistance between the PN junction and the shell surface, that is, the ratio of the temperature difference along the heat flow channel to the power dissipated on the channel. Junction temperature refers to the temperature of the PN junction of the LED

generally, the methods to measure the junction temperature and thermal resistance of LED include: infrared micro imager method, spectroscopy method, electrical parameter method, photo thermal resistance scanning method, etc. Using infrared temperature measurement microscope or micro thermocouple to measure the surface temperature of LED chip as the junction temperature of LED, the accuracy is not enough

at present, the commonly used electrical parameter method is to use the linear relationship between the forward voltage drop of ledpn junction and the PN junction temperature, and obtain the junction temperature of led by measuring the forward voltage drop difference at different temperatures