For total luminous flux calibration by a sphere-spectroradiometer system in 2π geometry, a new LED-based standard light source (standard LED) covering the full visible wavelength range has been developed. The developed standard LED has sufficient spectral power over the full visible wavelength range using UV-LED dies of different peak wavelengths in combination with red, green and blue phosphors. By evaluating spectrum flatness based on the magnitude of the second derivative, the spectrum of the standard LED was customised to minimise the measurement uncertainty. Properties of the standard LED such as the luminous intensity distribution, stability and reproducibility were also evaluated. The evaluation results indicate that the standard LED has good properties as a standard light source for the 2π total spectral radiant flux scale. Furthermore, the result of an operating current dependence suggests that the standard LED has benefits as a standard source that conventional standard lamps do not have.
This paper proposes a method for rendering objects coated with multilayer thin films, taking into consideration multiple reflection and refraction, interference, and absorption of light inside the films. The proposed method is based on wave optics, and it can accurately visualize the optical effects of multilayer films consisting of not only dielectric materials, but also metallic and semiconductive materials. Optical properties of a SiO 2 film coating on a silicon base, and several kinds of multilayer films coating windowpanes, glasses, or teapots are visualized to demonstrate the usefulness of the proposed method.
This paper proposes a method for rendering objects coated with multilayer thin films. Multilayer thin films are widely utilized in industry, for example, optical lenses, optical filters, and windowpanes, among others. Demand for visualization of the optical effects of multilayer films has therefore become great. To visualize optical properties of such films, we have developed a method for calculating composite reflectance and transmittance of the system of multilayer thin films, taking into consideration such factors as multiple reflection, interference and absorption of light inside the films. The proposed method is based on wave optics, and is able to accurately visualize the optical effects of multilayer films consisting of not only dielectric materials, but also metallic and semiconductive materials. Metallic and semiconductive materials are able to absorb light, and their refractive indices are expressed as complex values. Dielectric materials, on the other hand, do not absorb light, and the refractive indices are expressed as real values. Taking into consideration complex refractive indices, the proposed method can visualize optical phenomena caused by various kinds of multilayer thin films. The proposed method is implemented using a raytracer and optical properties of a SiO 2 film coating on a silicon base, and several kinds of multilayer films coating windowpanes or teapot are visualized to demonstrate the usefulness of the proposed method.
The National Metrology Institute of Japan realized a total spectral radiant flux scale in the visible wavelength range (from 380 nm to 780 nm) for sphere-spectroradiometer calibration in 2π geometry. For a transfer standard in 2π geometry, a standard source based on a specially-designed broadband light-emitting diode (2π standard LED) was used. For the scale realization, we used the goniophotometer/spectroradiometer system. In the realization, an effect of a bandpass function of the array spectroradiometer was corrected by a matrix inversion approach. The relative expanded uncertainty (k = 2) for the scale is from 3.3% to 5.7% depending on the wavelength range. We also evaluated the contributions of the wavelength calibration and the bandpass function to the measurement of the total spectral radiant flux of typical white LEDs against the 2π standard LED. Our results demonstrate that the 2π standard LED achieves uncertainties comparable to those of a conventional standard lamp, within a practical wavelength range for LED measurements. These results show that the 2π standard LED is a useful transfer standard for the realization of the total spectral radiant flux scale and for evaluation of the total luminous flux of LEDs in 2π geometry.
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