Hangzhou Zhejiang University Tricolor Instrument Co., Ltd. Abstract: The luminaire distribution photometer is a large-scale precision optical test equipment. It is currently available in several configurations. Based on the requirements of distributed photometric measurement, this paper analyzes the differences in the structure of existing distributed photometers and the problems in their application. Reasonable and comfortable lighting can not only meet the needs of people's daily life, but also provide a safe, energy-saving and efficient working environment. The distributed photometric performance of the luminaire is the most critical factor affecting the quality of the lighting. Using scientific testing methods and selecting the right instrument is the basis for obtaining accurate luminosity characteristics of the luminaire. The distributed photometric measurement of luminaires is an important part of quality control in luminaire design and lighting design. Especially with the development of new light sources and emerging lighting technologies, it poses new challenges for luminaire distribution photometric measurement. At present, there are various configurations of luminaire distribution photometers in the world, and different principle schemes are adopted to measure the spatial light distribution of lamps. Due to the difference in the level of technology of equipment manufacturers, there are various problems in the practical application of test equipment. Some commercial propaganda also mislead the user's understanding, so that the test data can not be applied to the actual lighting project, and can not be compared internationally. First, the basic requirements of distributed photometric measurement
1, photometric distance
The measurement of the luminous intensity is obtained by measuring the illuminance at a certain distance and calculating the intensity value according to the inverse square law of the distance of the photometry.
Ie: I(C,r) = E(C,r) * R2(C,r)
Where: I is the light intensity in the test direction, E is the illuminance of the photodetector receiving surface of the detector, and R is the test distance.
However, for many luminaires, especially LED luminaires, the near-field photometric law is not applicable. The CIE document specifies this. The luminosity test distance of the luminaire should be large enough to satisfy the following conditions [1][2]
For fluorescent lamps R>D × 10
For floodlights R>D × 200/θ
D: The maximum size of the illuminating area θ: The half-peak angle of the beam is usually two kinds of measuring distances: wide beam illuminator: 12m~15m, narrow beam high-intensity lamp 30m~35m, ensuring far field measurement accuracy.
2, photometric accuracy
The photometric detector is one of the important components of the distribution photometer. The spectral response S (λ) accuracy of the detector should be consistent with the optical visual efficiency function V(λ) of the human visual spectrum, ie S(λ) = V( λ). According to the International Commission on Illumination CIE regulations, for the measurement of the intensity distribution of gas discharge lamps, the V(λ) matching error f1' of the detector should not exceed 2%. To match the spectral response of the detector to the V(λ) curve, a set of filters of different materials is typically applied to the front of the silicon cell. Due to the spectral transmittance curve of the glass material, it is not easy to achieve an accuracy of less than 2% of f1'. Therefore, the probe of the high-precision distribution photometer needs to be imported from Germany. There are also some probes that use a partial filter method to achieve accurate V(λ) matching. This photometric detector is only suitable for the measurement of uniform beams. In the distributed photometric measurement, the spatial beam distribution is extremely uneven, and the detectors matched by some filter methods have a very large error in practical application.
At present, the sensitivity of the silicon photodetector used in the distribution photometer decreases with the increase of temperature, and the temperature changes by 1 °C, which will cause a sensitivity change of about 0.1%. In addition, the magnification of the photocurrent amplifying circuit is also affected by temperature. Therefore, the photometric probe and circuit must be kept at a constant temperature, and the temperature should be controlled within 1 °C.
3, angular accuracy
The distributed photometer tests the luminosity data of the luminaire in all directions, and has high requirements on the angular accuracy of the rotation and positioning system, including angular accuracy, axis accuracy, and mirror shape accuracy.
For distributed photometers with mirrors, the flatness of the mirror is very important. The shape error and angle mounting error will affect the angular accuracy by twice; the surface error will also affect the spatial characteristics of the measuring beam, causing greater measurement error. . If the measuring beam axis of the detector needs to be spatially rotated (conical) relative to the mirror during the measurement, the shape error of the mirror will affect the angular accuracy by four times. At present, the international high-end distribution photometer, the mirror and the frame are connected by special structure. The distribution photometer made by Zhejiang University and the German LMT company, the mirror is connected by local connection, and the parallelism of the mirror is laser-accurate. calibration. The mirror of some equipment adopts the direct bonding method, and the mirror flatness is difficult to ensure. The curing of the adhesive will cause stress in the mirror surface, causing the mirror coating to fall off and the mirror glass to have birefringence errors. In the long-term use, the steel frame will be deformed in time, causing permanent distortion of the mirror surface and not adjustable.
4, stray light
Stray light is one of the most important factors affecting test accuracy in distributed photometry. Adequate attention must be paid to the purchase of distributed photometric equipment and laboratory construction. It should be noted that there is also a few percent optical reflection on any black surface. The effect of stray light is especially noticeable for measuring narrow beam luminaires. For example, if the beam angle of the floodlight is 4°, even if the reflectance of the environment is only 1%, the influence of background stray light will cause the total luminous flux error to be more than 40%. . Therefore, the photodetector in the distribution photometer should only receive the light beam of the luminaire or the light beam reflected only from the mirror. Other stray light, such as the edge of the mirror, the ground, the wall surface, etc., should be eliminated. In the actual laboratory, a series of apertures should be set between the test fixture, the mirror and the probe. The aperture of the aperture corresponds to the aperture of the measurement beam, and the stray light of the environment is strictly controlled.
February 02, 2019