The range of the accuracy of scalar diffraction theory and effective medium theory for binary rectangular groove phase grating is evaluated by the comparison of diffraction efficiencies predicted from scalar theory and effective medium theory, respectively, to exact vector results calculated by Fourier modal method. The effect of element parameters (depth, period, index of refraction, angle of incidence, and fill factor) on the accuracy of scalar treatment and effective medium theory is quantitatively determined. Generally, it is found that the scalar method is valid when the normalized period is more than fourfold wavelength of incident light at normal incidence. The error of transmittances between vector method and scalar method increases as the incident angle and refractive index increase. Furthermore, when the higher diffraction orders other than zero-th order are not to propagate, the effective medium theory is accurate to evaluate the transmittance of grating at normal incidence. The error of transmittances between effective medium method and rigorous vector theory increases as the incident angle and refractive index increase. Also, the error of diffraction efficiencies between the simple methods and the vector method on the polarization state of incident light is clearly demonstrated.
The theory of mesopic vision provides an important theoretical foundation for the choice of road lighting sources. Based
upon a number of recent mesopic photometry studies, an equation (<i>E</i><sub><i>mes</i></sub> = <i>B</i>•<i>E</i><sub><i>P</i></sub>) to deduce from the <i>E</i><sub><i>p</i></sub> (photopic
illumination) to Emes (mesopic equivalent illumination) is proposed, where <i>B</i> is instant for modified coefficient. The
coefficient <i>B</i> can be used easily to calculate the mesopic equivalent illumination by using the measuring results of
photopic illumination for different correlated color temperature (CCT) light sources under mesopic light levels. Using
the equation, we analyze the variation of coefficient <i>B</i> with background lighting level of the different correlated color
temperature lighting sources under mesopic vision levels. By calculating the mesopic equivalent illumination of the
different sources, our results showing that the higher correlated color temperature LED sources have better visual effects.
Moreover, the results provide a basis for further studies on the illuminometer, which might be suitable for mesopic vision.
Photo-electronic imaging system is a discrete imaging system, according to Nyquist sampling theorem, if the maximum
spatial frequency is higher than Nyquist frequency, there is aliasing, and Morie fringe appears on image. The quality of
image is receded and the trueness of color depressed. An optical low pass filter (OLPF) used in front of photo-electronic
imaging sensor, can effectively limit the frequency spectrum width and critically satisfy Nyquist sampling condition.
Thereby, the aliasing will be eliminated and the quality of the image will be improved. This paper analyzes the
characteristics of frequency response of the OLPF and designs a novel system to measure the optical characteristic of the
OLPF. According to the characteristic of birefringent crystal, a light spot will be separated by the OLPF into several light
spots which will be processed by the computer. For the size of light point determined the limit of measurement accuracy
of OLPF's thickness, laser source, which can obtain light point with 2um diameter is used here as a target light point.
Magnified lens are used to improve the precision of the system. Other system used long working distance (WD)
microscope objective. Instead, this novel system uses the standard 100x optical microscope objective (WD<0.2mm) as
magnifying system. In this way, the cost of the system will be reduced in a great deal. The software of the system is also
very powerful, in addition to the basic function image caption and scanning, it can automatically detect the number of
light spots, distance and angles between light spots. The system can accurately measure the distance of point light at a
high resolution of 0.1um, and the measurable thickness of OLPF is from 0.5 to 5mm.