In order to develop visible thin film phosphors, we have for the first time prepared ZnCdS and ZnSTe doped with Iodine (I) using low-pressure MOCVD method. ZnCdS:I, of which Cd composition was calibrated to match the lattice constant to that of substrate and the band gap to absorption peak, showed a orange broad emission consist of yellow near band edge emission and red SA emission. Isoelectronic Te in ZnS indicates strong blue-green emissions, whilst I donor impurity in ZnS shows strong red SA emissions. A typical ZnSTe:I thin film shows two broad emission bands locating at around 500 and 680 nm, respectively, indicating Ra∼90. It was shown that high Ra thin film phosphor can be realized by single material (ZnSTe:I), and that MOCVD method is capable for controlling the thickness and doping profile to obtain uniform white emission pattern.

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Light Emitting Diode (LED) is expected as the lighting source of next generation because they are long life, small size, and low power consumption, etc. In previous paper, we proposed a simple visible-light transmission system for sound using white LED. However, the flicker of light is sensed if the transmitted sound signal has the low frequency component. In this study, we propose improved modulation technique to overcome the flicker. LED can transmit audio signal while it is used for lighting source. We verified that it is possible to communicate with the received luminous flux of 1.1×10^-5 lm without flicker. We also evaluated the effects of interference by plural LEDs.

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The amount of light captured by the eye depends on pupil size. Moreover, one of the factors determining the steady-state pupil size is ambient illumination and sudden increments of light reaching the retina cause a brisk and transient pupil constriction described as the dynamic Pupil Light Reflex response. In experiments where a glare source acts as transient conditioning field, a methodology to measure pupil diameter is required. In the present paper pupil diameter, in steady (0.5 cd/m²) and dynamic adaptation conditions, is measured. The dynamic state is originated by a transient peripheral glare source with three different illuminance levels (15, 30 and 60 lx). Ten eyes of 5 subjects (19, 36, 50, 53 and 52 years old) are considered. The measurements are made by means of a video of the pupil captured with a CCD while the sight is fixated in a chart. In the steady condition, the average pupil diameter for each subject varies between 4.8 and 7.2 mm from one subject to another. In the dynamic condition, latency time results to be independent both of the subject and of the glare level, adding evidence to the robustness of this parameter when radiation is not incident centrally.

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The perceived whiteness of 12 approximate white-color samples was evaluated under four different fluorescent lamps (EXD, EXN, EXWW, and EXL) using a paired comparison method, and then an interval scale was configured. Under all illuminations, the perceived whiteness of purple and red hue samples was highly evaluated while green and blue-green hue samples were poorly evaluated. The C/V index, a perceived whiteness evaluation index, which focused on the brightness-enhancement effect of color components that were included in the approximate white objects or illuminations, showed a high correlation with the interval scale value under each illumination. Furthermore, compared to various color appearance models, the index showed a superior predicting performance. The above findings confirmed that the C/V index was effective in evaluating the perceived whiteness of approximate white objects under different illuminations, and the brightness-enhancement effect of color components was an important factor in determining the perceived whiteness.

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We have proposed a new estimation method for a perceived brightness of a room based on the concept of the recognized visual space of illumination, or RVSI. We use the term ‘brightness size’ of the RVSI to express an observer’s perception of the intensity of illumination. We define the border luminance between the surface color and the unnatural surface color modes as the brightness size of the RVSI. Our previous work¹⁾ showed that the border luminance was proportional to the illuminance of a room and that was equal to the luminance of the brightest object in the room. We measured the border luminance in two differently decorated rooms to test the effect of the highest lightness of the object. One room was furnished with white walls and various lightness objects from black to white (environment N). The other was furnished with black walls and objects whose Munsell Values were 5 or less (environment L). Although the illuminances of the two rooms were the same, the border luminance in environment L was a half of that in environment N. Contrary to our previous result, the border luminance in environment L was higher than the luminance of the brightest object. We also compared the border luminance among between three different positions where the local contrast and the local illuminance were different. The border luminance was almost constant regardless of the measuring position, suggesting that the local environments have little effect on the perceived brightness of a room.

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Many white and nearly white objects are in our living and working areas, such as documents written on white paper, white curtains, white clothes, white walls, and white furniture. The perceived whiteness of these objects is important to the impression of the lighting in these areas. To investigate the perceived whiteness in living areas, a series of experiments were conducted using four different fluorescent lamps in three different environments. It was found that the areas of perceived whiteness in the living area environments were larger than the areas of perceived whiteness under achromatic conditions. Based on these results, a perceived whiteness index is proposed for these experimental conditions.

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