Eight common optical parameter detection techniques for LED lamps and lanterns
Published by Publisher: adminDate: 6/20/2024 9:04:13 PM Read: Detection of Optical parameters of LED Light Source.
1. Photometric determination.
The intensity of light, that is, the intensity of light, refers to the amount of light emitted at a certain angle. According to the CIE127 standard, the inverse square law is not applicable to the light emitting diodes because the light is concentrated. For the measurement of light intensity, CIE127 puts forward two conditions for measuring the average normal light intensity: condition A (far field condition) and condition B (near field condition). Both conditions are 1cm2. Generally speaking, the luminous intensity is measured by standard condition B.
2. Detection of luminous flux and luminous efficiency.
Light flow is the sum of the amount of light emitted by a light source, that is, the amount of light emitted. There are two main testing methods:
(1) Comprehensive method.
The standard lamp and the tested lamp are lit in turn in the integrating sphere, and the readings of the photoelectric converter are Es and ED respectively. When the standard light source flux Φ s is known, the measured lamp flux Φ D = ED Φ s/Es. The integration method adopts the principle of "point light source" and is easy to operate, but the measurement error is large due to the influence of the color temperature deviation between the standard and the lamp to be measured.
(2) Spectrometry.
The luminous flux is calculated by using the spectral energy P (λ) distribution. Using Monochromator, the 380nm~780 nm spectrum of the bulb is measured in the integrating sphere, and then the spectrum of the measured light is measured under the same conditions, and the luminous flux of the measured lamp is compared and calculated.
Luminous efficiency is the ratio of luminous flux emitted by a light source to power consumed. Constant current method is often used to measure the luminous efficiency of LED.
3. Spectrum characteristic detection.
The detection of spectral characteristics includes spectral power distribution, color coordinates, color temperature, color rendering index and so on.
The spectral power distribution represents that the light of the light source is composed of color radiation of multiple wavelengths, and the radiation power of each wavelength is also different. the order of the difference with the wavelength is called the spectral power distribution of the light source. The light source is measured by comparing the spectrophotometer (Monochromator) with the standard lamp.
The color coordinate is a digital representation of the number of luminous colors of the light source on the coordinate graph. Color coordinate diagram has many kinds of coordinate system, commonly used X, Y coordinate system.
Color temperature is a representation of the number of light source color tables (appearance colors) that people see. When the light emitted by a light source is the same color as the light emitted by the blackbody at a certain temperature, it is the color temperature. The color temperature in light is an important parameter to describe the optical properties of the light source. The relevant theory of color temperature is derived from blackbody radiation, and the color coordinates of the light source can be obtained from the color coordinates containing blackbody trajectories.
The color rendering index refers to the amount of light emitted by the light source that correctly reflects the color of the illuminated object, which is usually expressed by Ra. Ra is the arithmetic average of the color rendering index of the light source to eight color samples. Color rendering index is an important index of light source quality, which determines the application range of light source. Improving the color rendering index of white light LED is an important topic in the research and development of LED.
4. Determination of strength distribution.
The relationship between light intensity and spatial angle (direction) is called false light intensity distribution, and the closed curve connected by this distribution is called light intensity distribution curve. Because there are many measuring points, each point has to go through data processing, which is generally measured by an automatic distribution photometer.
5. The effect of temperature on the optical properties of LED.
Temperature has an effect on the optical properties of LED. Many experiments have shown that temperature has an effect on the emission spectrum and color coordinates of LED.
6. Measurement of ground brightness.
The luminance of a light source in a certain direction is the luminous intensity of the unit projection area in that direction. generally, the surface luminance is measured by surface luminance meter and aiming luminance meter, which can be divided into two parts: aiming light path and measuring light path.
Determination of other performance parameters of LED Lamp.
1. Measurement of electrical parameters of LED lamp.
The electrical parameters of LED lamp mainly include positive, negative and negative electrical parameters, which are related to the normal operation of LED lamp and are one of the bases to judge the basic performance of LED lamp. There are two methods to measure the electrical parameters of LED lamp: one is that the current is constant, the other is to measure the voltage parameters, and the other is to measure the current parameters when there is a certain voltage. Take the following measures:
(1) forward voltage.
When a positive current is applied to the detected LED lamp, there will be a voltage drop at both ends of the LED lamp. By adjusting the current value of the power supply, record the corresponding reading on the DC voltmeter, that is, the forward voltage of the LED lamp. According to the relevant common sense, when the LED is turned on, the resistance is lower, and the external method of ammeter is more suitable.
(2) countercurrent.
Apply a reverse voltage to the detection LED lamp, adjust the voltage stabilized power supply, and the ammeter reading is the reverse current of the tested LED lamp. Because the resistance of LED is high when it is turned on in reverse, the forward voltage of LED is measured by the method of ammeter interpolation.
2. Test of thermal characteristics of LED lamp.
The thermal properties of light-emitting diodes have an important influence on the optical and electrical properties of LED. Thermal resistance and junction temperature are the main thermal characteristics of LED2. The thermal resistance refers to the thermal resistance of the PN junction to the surface of the shell, that is, the ratio of the temperature difference on the heat flux channel to the dissipated power on the channel, and the junction temperature refers to the node temperature of the LED.
The measurement methods of LED junction temperature and thermal resistance generally include infrared microimage method, spectrum, electrical parameters, photothermal resistance and so on. Using infrared temperature measurement microscope or miniature thermocouple to measure the surface temperature of LED chip, the accuracy is not enough.
At present, the widely used electrical parameter method is to use the linear relationship between the positive voltage drop and the PN junction temperature, and to use the forward pressure drop difference of the LEDPN junction to obtain the LED junction temperature.
