1. Luminous intensity detection Light intensity is the intensity of light, which refers to the amount of light emitted within a certain angle. Due to the concentration of light from LEDs, the inverse square law is not suitable for short distances. The CIE127 standard provides two conditions for measuring the average normal light intensity: measurement condition A (far-field condition) and measurement condition B (near-field condition). The detector area in both cases is 1 cm2. Usually, the standard condition b is used to measure the luminous intensity
2. The detection luminous flux of two luminous flux and efficiency is the sum of the luminous flux emitted by the light source, that is, the luminous flux. The detection methods mainly include the following two kinds: (1) integral method. The standard lamp and the tested lamp are ignited successively in the integrating sphere, and their readings in the photoelectric converter are recorded as es and ED respectively. If the standard luminous flux is called φ s, the luminous flux of the lamp under test φ d = ed × φ s / es. The integration method is based on the principle of "point light source", which is easy to operate. However, due to the color temperature deviation between the standard lamp and the measured lamp, the measurement error is large. (2) Spectrophotometry. The luminous flux is calculated by the spectral energy P (λ) distribution. Using monochromator, the 380 nm ~ 780 nm spectrum of the standard lamp is measured on the integrating sphere, 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 efficiency is the ratio of luminous flux emitted by a light source to the power consumed. Constant current method is usually used to measure the luminous efficiency of LED.
3. The detection of spectral characteristics of LED includes spectral power distribution, color coordinates, color temperature, color rendering index, etc. The spectral power distribution means that the light of the light source is composed of many different wavelengths of color radiation, and the radiation power of each wavelength is also different. When light sources are arranged in order of wavelength, this difference is called the spectral power distribution of light sources. Compare and measure light source with spectrophotometer (monochromator) and standard lamp. Color coordinate is the amount of luminous color of the light source represented by numbers on the coordinate graph. There are many coordinate systems in the color representation, usually X and Y coordinate systems are used. Color temperature is the number of light source color tables (appearance color representation) seen by human eyes. When the light emitted by the light source is the same color as the light emitted by the * * blackbody at a certain temperature, the temperature is the color temperature. In the field of illumination, color temperature is an important parameter to describe the optical characteristics of light source. The relevant theory of color temperature is derived from blackbody radiation, and can be obtained from the color coordinates of the light source including the blackbody track. The color rendering index indicates the amount of light emitted by the light source that correctly reflects the color of the illuminated object. It is usually represented by the universal color rendering index RA, which is the arithmetic mean of the color rendering indexes of eight color samples. Color rendering index is an important parameter of light source quality, which determines the application range of light source. To improve the color rendering index of white LED is one of the important tasks of LED research and development.
4. The influence of temperature on the optical properties of LED temperature will affect the optical properties of LED. A large number of experiments show that temperature can affect the emission spectrum and color coordinates of LED.
5. The electrical parameters of LED lamp mainly include forward voltage, reverse voltage and reverse current, which are related to the normal operation of LED lamp and are one of the bases for judging the basic performance of LED lamp. There are two kinds of electric parameter measurement of LED lamp: voltage parameter under certain current and current parameter when voltage is constant. The specific methods are as follows: (1) DC voltage. When the forward current is applied to the LED lamp to be detected, a voltage drop will occur at both ends of the LED lamp. Adjust the power supply determined by the current value and record the relevant reading on the DC voltmeter, which is the DC voltage of the LED lamp. According to the relevant common sense, when the LED is positively conducting, the resistance is small and the external connection method of the ammeter is more accurate. (2) Reverse current. Apply reverse voltage to the tested LED lamp and adjust the regulated power supply. The ammeter reading is the reverse current of the LED lamp being measured. Similar to the DC voltage measurement, the LED is connected internally with an ammeter due to its large resistance when reverse conducting.