In the display industry, the hottest battle is the dominance of OLED and LCD. Due to the many advantages of OLED in optics, it is considered as the next-generation technology of display screens. It will gradually replace LCD as the mainstream of display screens in the future. The optical advantages of OLED are: higher color gamut, more vivid colors; better viewing angle, no obvious color shift in large viewing angles; faster response time, no tailing phenomenon when watching dynamic pictures; self-luminous, darker state, darker, No light leakage, theoretically 0 can be achieved, and the contrast will be higher. The R&D department of the above optical parameters needs to use optical instruments for measurement and adjustment. The module factory will also conduct random inspections before shipment for quality monitoring. The same customers will also conduct random inspections to ensure that the products meet the optical standards. Optical measurement inspection is an important part of the display industry's industry chain. component. For the optical measurement and detection of a single point, two types of optical instruments are basically used, namely colorimeters and spectrometers. This article focuses on the similarities and differences in the functional principles of these two instruments.
one. Same point
In a simple summary, the similarity between the colorimeter and the spectrometer is that both can measure the brightness and chromaticity of the display, and then calculate other parameters, such as dominant wavelength, correlated color temperature, color purity, etc., of course, according to the brightness and chromaticity Can further calculate the penetration rate, contrast, depending on the role of deviation and so on.
two. difference
1. First introduce the functional principle of the spectrometer: as the name suggests, the spectrometer is naturally an instrument that can measure the spectrum. This is also the biggest difference between it and the colorimeter. The colorimeter cannot measure the spectrum. We know that light is an electromagnetic wave. To understand the characteristics of light in detail, you need to know its spectrum. Light is composed of electromagnetic waves of different intensities and wavelengths. The most commonly used spectrometers generally have three bands, ranging from small to large. Followed by ultraviolet light, visible light, and infrared light. For the display screen, we mainly focus on the spectrum in the visible light range (380nm-780nm).
The basic principle of the spectrometer is: using a grating to decompose a mixed light into light of different wavelengths, and the light of different wavelengths will be measured by different detectors to obtain the spectrum of the measured light. After obtaining the light spectrum, we According to the spectrum, the brightness, chromaticity, peak wavelength, color rendering index (CRI), etc. can be obtained. In fact, with the spectrum, all the parameters of the light at this moment can be obtained. The spectrum is the king.
So how to get the brightness and chromaticity of light according to the spectrum? According to the formula of CIE1931XYZ system to calculate the tristimulus value: the tristimulus value can be obtained by multiplying the spectrum by the integral of the CIE1931 standard observer characteristic curve. For luminous bodies such as display screens, the spectrum can be used directly. For reflected light, the spectrum is equal to the spectrum of the light source multiplied by the reflection characteristic spectrum of the object. The spectrum is an absolute physical quantity, while brightness and chromaticity are physical quantities subjectively perceived by humans and are related to human physiological characteristics. This involves the sensitivity characteristic curves of the three photoreceptor cells in the human eye to different wavelengths of light. Scientists have obtained experimental results The average sensitivity characteristic curve of three kinds of photoreceptor cells of human beings to different wavelengths, namely the CIE1931 standard observer characteristic curve.
The spectrometer needs to decompose light into light of different wavelengths, and then measure its intensity separately, which results in a relatively slow measurement speed. For parameters that require a large amount of data to be calculated, such as LCD screen flicker and liquid crystal response time, these two In the parameter industry, colorimeters are generally used for measurement.
2. The following focuses on the principle and function of the colorimeter. Compared with the spectrometer, the colorimeter has no grating, it cannot split light, nor can it measure the spectrum of light, but the colorimeter has a special filter, namely XYZ filter. Simulates the CIE1931 standard observer characteristic curve, the light is detected by the detector after the filter, and then through some special circuits for ADC conversion, the final result is the integral value of the overall light, which is similar to the calculation method of the above CIE1931XYZ system to calculate the tristimulus value , But it is done through physical hardware.
Since there is no need for spectroscopy, the measurement speed of the colorimeter is very fast, but there is still about 2% difference between the best XYZ filter in the world and the CIE1931 standard observer characteristic curve, so the brightness and chromaticity measured by the colorimeter will be different. The degree of error is determined by the colorimeter itself and the spectral characteristics of the measured screen. In order to obtain accurate data, the colorimeter needs to be corrected for different batches of screens, and the correction data of different batches should be saved in Different correction channels. Generally, the data measured by the spectrometer is used as the standard data. After calibration, the data measured by the colorimeter and the spectrometer are basically the same, while maintaining the advantage of faster measurement speed, while the spectrometer only uses the standard light source for correction before leaving the factory. Afterwards, for different samples, no correction is needed, and the measured value is the standard value.
three. Summarize
1. Both colorimeters and spectrometers measure brightness, chromaticity and the color temperature, dominant wavelength, color purity, etc. that can be calculated from this.
2. The colorimeter has fast measurement speed, which can measure flicker and liquid crystal response time, but the spectrometer can't, but the spectrometer can measure the spectrum and calculate the color rendering index, peak wavelength, etc., but the colorimeter can't.
3. The spectrometer does not need to be corrected after leaving the factory, and the colorimeter needs to be corrected for different batches of screens to get accurate values. Spectrometers are slower, more accurate, and more expensive. University research institutions and company R&D departments have more applications, while colorimeters are faster and relatively cheap, and are more often used in factory production lines.