Photometric Integrating Sphere> The basic principle is to make the light source illuminate the center of the sphere to emit light, and the emitted light will be diffusely reflected to the coating on the inner wall of the sphere. Diffuse light will pass through the diffuse reflection and continue to cycle until the light flux is consistent across the entire inner surface of the sphere. A probe mounted on the wall of the sphere then reads out the luminous flux emitted by the light source.
1. The structure and basic principles of the photometric integrating sphere>
The photometric integrating sphere can only be used to test the color temperature, luminous flux, color coordinates, color tolerance, luminous effect and spectral band of the omnidirectional light source. Color tolerance refers to the difference between the X and Y values calculated by the photochromic and electrical detection system software and the standard light source. The smaller the value, the higher the accuracy. Luminous efficacy refers to the ratio of the total luminous flux emitted by the light source to the electrical power (watts) consumed by the light source, and the unit is lm/w. For example, the total luminous flux of lamp A and lamp B is both 100lm, the power consumption of lamp A is 10W, and that of lamp B is 20W, then it can be considered that lamp A is more energy-efficient than lamp B.
The basic principle of the photometric integrating sphere> is to let the light source shine in the center of the sphere, and the emitted light hits the coating on the inner wall of the sphere to produce diffuse reflection, and the diffusely reflected light is then diffusely reflected. Continuously circulate until the luminous flux on the entire inner surface of the sphere is consistent, then what the probe installed on the sphere wall reads is the luminous flux emitted by the light source. However, the premise of obtaining this result is that there must be a partition coated with the same coating between the probe and the light source to prevent the light from the light source from directly shining on the probe. The integrating sphere in the laboratory is a hollow sphere made of cast iron. The inner wall is coated with a white rough coating. The main component is barium sulfate. It is mainly used to produce diffuse reflection and make the light intensity of the entire spherical surface consistent. There are openings on the wall of the ball for installing the probe, and the probe is connected to an external high-precision fast spectroradiometer.
Integrating spheres for state-of-the-art laboratories have an optical probe attached to them. Probes allow measurement sampling. There is a baffle coated with the same coating as the inner wall of the ball between the light source and the probe, besides, there are also brackets and lamp holders for installing the lamp tube inside the ballbracket. The power supply of the light source in the sphere is provided by an external AC regulated power supply, and a power meter is connected to monitor the electrical parameters at the same time.
Integrating spheres in the laboratory mainly have diameters of 0.3m, 0.5m, 1m, 1.5m, 1.75m and 2m. During the test, different diameters of integrating spheres should be selected according to different lamps for testing.
2. Measurement method of photometric integrating sphere>
1. Relevant definitions Background signal: It can be understood as some clutter signals that are still output in the system when there is no signal input. For example, if the light source is not turned on in the integrating sphere and the sphere is sealed, the readout luminous flux should be 0, but in fact some small signals can still be read out, which can be considered as background signals. Detection limit: refers to the minimum limit that can be measured by equipment or measurement methods. When using the device, in order to avoid background signal interference, it is usually necessary to zero out first, that is, to filter out the background signal. In other words, all signals smaller than the background signal will be filtered out, that is, the background signal can be understood as the detection limit of the device. Standard lamps: Various electric light sources used to reproduce and maintain units of luminosity and radiometric measurements and value transfer. They are standard gauges in optical radiometry, that is, calibrated luminaires that emit a fixed luminous flux under calibrated conditions (specific current or specific voltage).
2. Measurement method
Photometric Integrating Sphere> is measured by the relative comparison method. The actual measured value is calculated by comparing with the standard lamp. Therefore, it is generally necessary to use the standard lamp to calibrate before measurement. Calibration means to use standard lamps to let the equipment establish a standard for comparison with the actual measured value. In fact, the calibrated equipment is inspected with different standard lamps, and the characteristic values obtained still have certain errors.
3. Test steps
3.1 Preparation before the test
(1) Select an integrating sphere of appropriate size according to the size of the lamp;
(2) According to the luminous flux of the lamp light source, select the closest standard lamp for inspection and calibration;
(3) During the test, the wind from the air conditioner should not be blown directly to the integrating sphere. First, because the wind blowing on the integrating sphere will cause fluctuations in the surface temperature of the sphere. Second, because the temperature of the filament will be relatively high when the standard lamp is lit. The cold wind blowing on the lamp during the ball will shorten the service life of the lamp.
3.2 Start the test
(1) Inspection. The equipment should be inspected before use, and a standard lamp with a luminous flux similar to the test sample should be selected during the inspection. It should be noted that when selecting a standard lamp, it depends on the measurement date and measurement cycle of the standard lamp. If the date is exceeded and there is no measurement, the standard lamp is out of control and cannot be used. After passing the inspection of the measurement certificate, install the standard lamp in the optical integrating sphere, connect an external DC power supply and a power meter, and light the standard lamp with the current (voltage) stated on the measurement certificate. When installing, ensure that the lightThe source is at the center of the optical integrating sphere. Then test continuously in the middle of the software operation interface until the measured luminous flux reaches a stable value and read out the luminous flux value. It is generally believed that the change of luminous flux within 5 minutes does not exceed 0.5% to reach a stable state. During continuous measurement, it takes 23s for one measurement, and it can be calculated according to the number of measurements whether it reaches the stable standard. When using a DC power supply, it should be noted that in the steady current mode, the current and voltage are adjusted at the same time, but the current should be adjusted slowly, and the voltage should be adjusted quickly. Although the DC power supply comes with a voltmeter and ammeter, if it is not measured, it is impossible to be sure that the voltage and ammeter display is correct, so an external power meter is needed to monitor the electrical parameters. If the inspection shows that the luminous flux is within the uncertainty range declared by the equipment, then the equipment can be used directly if it passes the inspection; otherwise, it shall be calibrated.
(2) Calibration. A standard light source is selected for calibration and calibration. The optical integrating sphere needs to be calibrated for luminous flux and color temperature before it can be used normally. In addition to the calibration that needs to be performed if the inspection fails, it is also necessary to re-calibrate when the original test conditions are changed such as changing the test settings in the software, changing the probe, etc. The operation before calibration is similar to the inspection, but there is a difference that after the standard lamp is installed, it must be cleared before lighting. Except that the standard lamp does not need to be lit when clearing, the other conditions are the same as during the test. After the zeroing is completed, turn on the standard lamp according to the conditions on the measurement certificate. After the luminous flux emitted by the standard lamp is stable, enter the standard luminous flux and standard color temperature of the standard lamp in the software operation interface, click Start Calibration, and the device will automatically complete the calibration.
(3) After the calibration is completed, the test can only be started after checking again.