Journal of Light
&
Visual Environment

Volume 28 Number 2, August 2004

CONTENTS

Papers

Research Note

Letters

Laboratory Review

English Abstracts

 To facilitate the application of tri-chromatic white LEDs, we developed a Ca(Eu_1-xLa_x)₄Si₃O₁₃ red phosphor that emits red light at a peak wavelength of 613 nm when it is excited by near-ultraviolet rays at a peak wavelength of 395 nm. The activator concentration dependence of the light conversion efficiency showed that the optimum composition of the red phosphor was at x=0.5 and that the conversion efficiency was 0.14. When a near-ultraviolet LED with an assumed external quantum efficiency of 0.40 was combined with Ca(Eu_0.5La_0.5)₄Si₃O₁₃ red phosphor and existing green and blue phosphors, the calculated luminous efficacy and general color rendering index of the resultant white LED were 21.6 lm/W and 83.9, respectively.

KEYWORDS : CaEu₄Si₃O₁₃, red-emitting phosphor, Eu3+ ion, near-ultraviolet, white LED, semiconductor lighting

 The visual experiment on perceived colour difference is conducted using 160 colour chips of various hues arranged on a closed hue circle of constant chroma C = 6 and of constant value V = 6. Correspondence between perceived colour difference and predicted colorimetric colour difference obtained by various colour difference formulae in several colour spaces is examined.
The examination is conducted on uniform colour spaces CIELUV, CIELAB, NC-IIIC and L*a*b*-N, colour appearance model CIECAM97s, and colour difference formulae CMC, CIEDE94 and CIEDE2000.

Results obtained are as follows:
1) In uniform colour spaces NC-IIIC and L*a*b*-N, predicted colour difference has good correspondence to perceived colour difference. These two uniform colour spaces are implemented with proper non-linear compensation in opponent response process and thus they are significantly superior to other colour spaces in the geometrical uniformity of colour specification.
2) In uniform colour spaces CIELUV and CIELAB, it can be stated that non-uniformity in hue difference is caused by the fact that hue and chroma axes are not perpendicular and the fact that hue and chroma are not independent, both of the above facts originating from the lack of compensation mechanism in opponent response process.
3) The revised colour difference formulae based on the uniform colour space CIELAB, namely CMC, CIEDE94 and CIEDE2000, do not create an improvement to colour difference characteristics compared to the original colour space CIELAB.
4) When designing a uniform colour space or a colour difference formula that ensures accurate colour difference evaluation, it is essential to construct the uniform colour space in which hue, lightness and chroma axes cross at right angles so that all elements (hue, lightness and chroma) can be independently evaluated and attached weight by introducing proper non-linear opponent response functions.

KEYWORDS:colour-difference, uniform colour space, perceived colour-difference, hue scale, NC-IIIC, L*a*b*-N

 Two aspects of UV photobiology have come up almost simultaneously for discussion. On the one hand, the CIE has, for all practical purposes, completed discussions of a new standard “CIE S 009/E: 2002 Photobiological Safety of Lamps and Lamp Systems”¹), and it was adopted without any amendments. On the other hand, some national standards (for example, in Russia) have for decades insisted on UVA+UVB radiation being used for prophylactic purposes at actinic erythemal doses (around 140 J m^-2 per 8 hours of irradiation), which are significantly higher than prohibitive doses of actinic UV hazard (30 J m^-2) suggested in the CIE standard.
It seems that this arisen situation is to be thought about more carefully.

KEYWORDS :prophylactic UV radiation, erythema, UV hazard exposure limit for the skin, exposure time

 A thin-film diamond UV sensor is a solar-blind photo detector sensitive to only vacuum ultraviolet regions. We have used this sensor to measure the intensity of vacuum ultraviolet light emitted from a xenon excimer lamp, a short-wavelength light source, and the sensor has shown stable sensitivity over 98-hour radiation with an irradiance of 10mW/cm² of xenon excimer lamp. Therefore, the diamond UV sensor is promising as a photo detector able to measure vacuum ultraviolet radiation, the use of which is increasing.

KEYWORDS : diamond UV sensors, solar blind, sensors package, highly oriented diamond films, vacuum ultraviolet

 Our research purpose is to build an artificial neural network with an excellent color discrimination capability like human being on a computer. In this study, we built the network, which was trained to learn 10 colors with different hues in the Munsell color system. Then, we examined the response of the trained network when the network was interrogated about 10 non-learned colors. The network showed a good color discrimination capability, close to that of human being.

KEYWORDS : color discrimination, artificial neural network, spectral reflectance distribution,
Munsell color system

  In DALI control, a small built-in chip acts as the de-central controller in the ballast. DALI complies with an open source protocol based on standard IEC60929. One small controller controls up to 64 ballasts. Today, manufacturers are adding more devices, such as sensors, blind motor controllers, and switches. Recently, web browser based remote control was developed for the DALI Lighting Laboratory at Pennsylvania State University. This paper reports on first experiences with advanced DALI features.

KEYWORDS : digital addressable lighting interface DALI, lighting control, remote web browser control, color mixing