The research and development of the light source has become the focus of the world. Requirements, various product quality supervision, third-party testing and professional certification agencies, and enterprises themselves have new demands for testing equipment. There is still no unified test method for the measurement of light and color characteristics of LEDs and their finished lamps. At present, most of them use integrating spheres or goniophotometers to measure the optical characteristics of LEDs. The goniophotometer test system has high precision, but it is very expensive, the operation is complicated, and the measurement time is long, which takes 6-8 hours, which cannot meet the actual production test needs of small and medium-sized enterprises. Using an integrating sphere to test the system has low precision, but it is cheap, easy to operate, and has a fast measurement speed. A single measurement only takes about 30 minutes. However, because there is no dedicated LED standard light source, the reliability of the measurement results is low. To this end, we use the integrating sphere test system to test the light and color characteristics of the LED/COB ceiling lamp by placing the integrating sphere at different positions and facing different angles, and then use a high-precision goniophotometer to test the same LED/COB ceiling lamp. Test related light and color parameters, and then study and analyze the influence of different angles on the test of LED integrating sphere>
1. Optical characteristics and positional relationship of LEDs>
Traditionally packaged LEDs are generally circular or cylindrical, and their light-emitting angle is 5°～90°. Moreover, the light intensity distribution of the LED light source is uneven, that is, the light intensity in the normal direction is the largest. As the angle between the light-emitting direction and the normal direction increases, its light intensity is an approximate Lambertian light source, and its light-emitting area is relatively small, that is, the brightness of the LED light is the largest when it is distributed in a certain direction, and the light is vertical at this time. On the light-emitting surface of the LED, that is, the angle with the axial direction is zero degrees, and the brightness will decrease as the angle increases.
Second, LED Integrating Sphere Measurement Principle
>The integrating sphere test system measures the luminous flux, spectral distribution and chromaticity of LED light source by relative method. Calibrate the integrating sphere photometer and spectroradiometer with the same type of standard light source for the LED to be tested to obtain better measurement uncertainty. This test uses theNarrow beam angle D65 standard light source calibrated for LEDs. Using the integrating sphere test method, placing light sources, screens, brackets and other objects in the integrating sphere will change the light distribution in the sphere and form a self-absorption effect. When the lamp is in different positions or angles, the light distribution in the ball is also different. During the test, the light source is usually placed in the center of the integrating sphere, and the luminous flux and average spectral power distribution of the light source are measured respectively through the photometer and spectroradiometer arranged in the detection window of the integrating sphere, and the spectral correction factor is calculated according to the measurement results and the luminosity is corrected The measured value of the meter is used to calculate the spectral correction factor.
Third, Goniophotometer Measuring Principle>
On enough light-emitting planes, measure the photometric detector of the goniophotometer to the object with a small enough angular interval Measure the illuminance of each point on a virtual spherical surface whose distance between the centers of light emission of the LED light source is the radius. The angular interval between planes is generally 5°, and the angular interval within a plane is generally 1°. When the size of the LED module to be tested is large or the beam angle is narrow, a smaller plane interval and angle step should be used to ensure the illumination distribution. sampling integrity.
Fourth, test phenomenon>
(1) Luminous flux. When the COB ceiling light is placed facing forward, although the detector is blocked by the baffle, some light still shines directly on the detector, so the maximum measured value is 235.62lm; while when the COB ceiling light is facing backward, the light is diffusely reflected When irradiated on the detector, the minimum measured value is 219.38lm, and the extreme value difference is 16.24lm.
(2) Color temperature. The color temperature is related to the chromaticity coordinates, the color temperature value increases, and the color becomes cooler. When the LED light is facing forward, the maximum color temperature measurement value is 6661.4K, the upward measurement value is 6268.2K, and the downward measurement value is 6219.2K. In other cases, the difference from the downward measurement value does not exceed 1%.
(3) Color rendering Ra. The spectrum determines the color rendering. When the spectrum of each band is continuous and rich, the color rendering is better; when the light waves in some bands are missing or less, the color rendering is poor. When the COB ceiling light is facing forward, the maximum color rendering is 85.18, and when it is facing backward, the color rendering is minimum 83.94, with a difference of 1.24 between the extreme values.
(4) Light effect. The distribution change and luminous flux of the measured value of the light effect at different angles are basically the same. When the COB ceiling light is facing the front, the measured value of the light effect is the largest, which is 82.28lm/W; when it is facing away from the baffle, the measured value of the light effect is the smallest, which is 75.66lm/W. The extreme value difference is 6.62lm/W.
(5) Dominant wavelength. The dominant wavelength reflects the difference between the spectrum of the light source to be measured and the bulk spectrum of the standard light source. The measured dominant wavelength of the COB ceiling light is at least 475.4nm when it is facing forward, and the measurement results in other cases are not far from the measurement results when it is placed downwards, and the measured value when placed downwards is 479.68nm.
The test results show that for the LED light source, due to the inhomogeneity of its own light emission, its spatial luminosity and chromaticity parameters are different. There is a certain gap in the comparison and analysis of the measurement results of the photometer test system, but the gap is not large. In view of the characteristics of fast measurement speed, easy operation and low price of the integrating sphere, it is recommended to use the LED integrating sphere> test system for the measurement of LED finished lamps, and place it at the downward position of the center of the integrating sphere. The parameters are compensated accordingly.