Spectrometer> is the basic test equipment for the measurement of illumination photometric and colorimetric parameters, accompanied by instrument science, electronic technology and With the development of software information technology, spectrometers are also undergoing changes. Lighting products have led the transformation of light sources from the initial incandescent lamp to gas discharge lamp, fluorescent lamp, HID to the current LED lighting; and professional spectrometers are gradually meeting the measurement needs of LED lighting, providing accurate information for the application design of LED lighting. information played an important role. The development of intelligent lighting, color adjustment and wireless technology has brought unlimited opportunities for LED lighting. In terms of realizing energy-saving and accurate lighting effects, spectrometer technology plays an important role in the field of LED lighting.
A spectrometer> is a device used to measure the spectral power distribution of a light source . It can be combined with corresponding light collection devices (such as integrating sphere, diffuser, light intensity sampling device, brightness sampling device, etc.) to measure photometric parameters such as luminous flux, illuminance, light intensity and brightness, as well as chromaticity coordinates, correlation Chromaticity parameters such as color temperature and color rendering. These photometric and chromatic parameters are important metrics for lighting applications and appliances. In addition, other parameters can be obtained by weighting the spectral power with a specific functional efficiency function. For example, photosynthetically active radiation (PAR) can be obtained by weighting spectral irradiance and plant photosynthesis curve, and blue-light hazard-weighted radiance can be obtained when spectral irradiance is weighted by the retinal blue-light hazard function.
A spectrometer> for measuring light sources generally includes multiple parts such as an incident slit, a collimation system, a dispersion system, an imaging system, and a photodetector. Among them, the classification of dispersion components includes prisms and gratings, etc., and because gratings are easier to obtain uniform dispersion, most spectrometers use gratings. According to the different sampling components of the spectrometer, it can be divided into a monochromator mechanical scanning spectrometer and a fast spectrometer based on an array detector.
A monochromator is usually composed of an incident slit, a collimating mirror, a grating, a converging mirror, and an exit slit. Only a certain monochromatic light passes through the exit slit, and then a single-channel photodetector is placed The meter measures energy. The mechanical scanning structure can realize the scanning of different bands, but it requires a long measurement time.Measurement time, while the overall stability is poor, easily affected by temperature, frequent calibration is required to ensure accuracy. Usually this kind of spectrometer is only used in the laboratory, especially in the measurement of LED lighting, which shows higher capabilities and advantages.
A fast spectrometer> based on an array detector is a new spectroscopic technology, which uses multi-channel detectors such as CCD and PDA to replace the exit slit in a mechanical scanning spectrometer And a single-channel detector, so that it can accept all the dispersed light signals in the measurement wavelength range at one time, so as to realize the fast measurement of milliseconds. The fast spectrometer has the advantages of small size, stable overall structure, and can save calibration time, etc., so it plays an important role in small and compact laser systems. However, the control of stray light is also an important challenge and must be effectively suppressed by appropriate methods.
A spectrometer is a measuring instrument that has appeared and developed in recent decades. Since the mechanical scanning spectrometer> is described in CIE 63-1984 and its subsequent standards, and the fast spectrometer was also added in the North American standard LM-58 in 2013 about the performance characterization and determination of this type of instrument The requirements of the labeling method. For spectrometers, the most important technical indicators include: spectral resolution, stray light, dynamic range, wavelength accuracy and sensitivity, etc. To evaluate the performance of fast spectrometers, the International Commission on Illumination (CIE) established Technical Committee TC2-51.
Spectral resolution refers to the ability to distinguish two very close spectral lines based on the Rayleigh criterion. That is, the central diffraction maximum of the first spectral line is located on the first-order minimum of the second spectral line. If the spectral resolution of the spectrometer is small, it will cause the measurement broadening of the spectral line and the reduction of the peak wavelength power. Spectral resolution can be characterized by bandwidth, which is composed of a bandpass function composed of the response function to the incident slit, the response function of the pixel, and the optical transfer function. The bandwidth information can be obtained by measuring the characteristic spectral line or the half-peak width of the laser. Spectral resolution and reading resolution (sampling interval) need to be distinguished, and the former generally needs to be lower than the latter.
Stray light is one of the main reasons affecting the measurement accuracy, which can be divided into near-field stray light and far-field stray light. TC2-51 adopts the band-pass color wheel technology suggested by Yuanfang Optoelectronics to evaluate far-field stray light. Especially in the short wavelength part (ultraviolet to blue light) its measurement affects most. Since the responsivity of the S detector in the short-wave part is much lower than that in the long-wave part, the light radiation intensity of the standard A light source in the red part is much higher than that in the blue part, so the calibration spectrometer> may be in the blue part Overestimate the spectral power, so stray light will also bring errors when measuring LED light sources. Monochromators have less stray light, but now fast spectrum stray light can also be corrected to a low level.