Journal of Light & Visual Environment
Online ISSN : 1349-8398
Print ISSN : 0387-8805
Volume 34 , Issue 2
Showing 1-9 articles out of 9 articles from the selected issue
Papers
  • Emilia RAUTKYLÄ, Marjukka PUOLAKKA, Eino TETRI, Liisa HALONEN
    2010 Volume 34 Issue 2 Pages 59-68
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    There is previous evidence that using high correlated colour temperature (Tcp), white light can improve concentration and alertness, resulting in better productivity in office environments. In this study, it was investigated whether the same applies to students exposed to light, while attending lectures. The study consisted of two sequential field studies, conducted during spring and autumn. The subjects were exposed to light provided either by 4,000 K or 17,000 K T5 fluorescent lamps for 90 minute lecture periods. The subjects were asked to judge their level of alertness on a 9-step scale at the beginning, and then at the end of each period. In spring, no change in alertness during the lecture period was detected. There was neither shown correlation between the Tcp of light and subjective alertness. Instead, the study in autumn found that the decrease in alertness during lectures was significant, and post-lunch dip effect appeared strong in the afternoon. The autumn study indicated that exposure of the subjects to a 17,000 K light source in afternoon lectures, potentially assists students to maintain higher levels of alertness, as compared with the results of the 4,000 K light. This study therefore suggests that the colour temperature, and the timing of the light exposure, play important roles in student alertness in lecture room environments.
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  • Yoko MIZOKAMI, Hirohisa YAGUCHI
    2010 Volume 34 Issue 2 Pages 69-75
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    We are surrounded by a variety of color distributions, which change greatly according to the surrounding environment. It is not yet well understood how much the appearance of objects is influenced by these color distributions in the surrounding environments. Brown and MacLeod (1997) showed that color appearance depends on the chromatic surround variance; this is known as the “gamut expansion effect.” However, Brown and MacLeod used relatively small patterns on a monitor. Whether the same effect would be obtained in an actual room environment has not been investigated. We examined whether the colorfulness perception of an object is influenced by the chromatic variance of its surroundings in a normal environment such as a room with furniture and objects inside. Two miniature rooms, one with gray and one with color-saturated objects inside, were placed side by side and used as a reference and a test room, respectively. Observers compared the colorfulness of a small square patch placed in the reference and the test rooms. The results showed that the apparent colorfulness of a patch was generally lower when it was closely surrounded by color-saturated surfaces, suggesting that the color appearance was changed slightly by the influence of other saturated objects in the room. However, the shift was very small, implying that chromatic surround variance has little influence on color appearance in an actual environment.
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Letters
  • Yoshinari ISHIDO
    2010 Volume 34 Issue 2 Pages 76-81
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    By using the series solution of the effective emissivity in a semi-infinite cylindrical cavity with respect to a wall reflectivity shown in our previous literature, it can be analyzed theoretically that normally directed emission of the cavity from its aperture to a disk-type receiver holding a centerline in common with. Applying the results of this analysis, it can be evaluated that the hemispherical emissivity of a plane source with nano-sized cavities or tubes array that is consist of high-emissive material, such as carbon nanotubes. In some experiments, as high-density nanotubes are used, the represented single cavity is available; however, it cannot predict the top data by fabricating low-density nanotubes but can predict, considering the horizontal interreflection of fluxes penetrating the cavity's wall.
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  • Yufang ZHANG, Warren G. JULIAN, Terry A. PURCELL
    2010 Volume 34 Issue 2 Pages 82-86
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    Previous research has shown that contrast sensitivity improves progressively as adaptation luminance is increased. This paper proposed to use simulation as a direct way to show the effect of change of adaptation luminance upon contrast sensitivity. Matlab software was used in the simulation and 14 pictures were simulated. 10 pictures of the 14 pictures were processed to filter certain spatial frequencies of the luminance. 20 subjects answered word lists to evaluate the environment of the simulated pictures. The most important finding was that the effect of change of adaptation on contrast sensitivity can be simulated and shown in a direct way. It was concluded that in lighting research, an alternative approach for doing experiments can be doing experiments in a simulated environment. It implied that in interior lighting design, energy saving should not be an excuse to deprive people's well-being.
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Technical Trend
  • Tse-ming CHUNG, Roger T.H. NG
    2010 Volume 34 Issue 2 Pages 87-93
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    This paper describes a study on the variation of calibration factor over time for High Dynamic Range (HDR) photography in a single daylit interior scene. Field measurements were conducted in a classroom under stable sky conditions. The luminance of each color of the X-Rite ColorChecker chart measured with a calibrated luminance meter was compared with the luminance value of the corresponding pixels extracted from the HDR image fused with low dynamic range (LDR) photographs of multiple exposures taken using a consumer grade digital single-lens reflex camera fitted with an ultra wide angle lens. The ratio between the luminances obtained from these two methods was computed and defined as the calibration factor. It was found that for each color there was a weak and not significant correlation between the calibration factor and the daylight levels ranging from about 75 to 30,000 lx. Without any significant relationship with the daylight levels, the calibration factors of each color obtained in the measurements were averaged, so that for any daylit scene with a dominant color, the real luminance could be determined by multiplying the average calibration factor of that color to the HDR luminance. The calibration factor of a ‘daylit scene’ in which all the 24 colors were evenly distributed was also computed, and it was 0.53 with a standard deviation of 0.03. Having more understanding about the feasibility of applying HDR photography technique as a luminance data acquisition system, researchers can have more confidence in its application for the investigation of the relationship between various luminance-based parameters and interior daylighting performance.
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Technical Reviews
  • Alex J. SHEPHERD
    2010 Volume 34 Issue 2 Pages 94-100
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    This study investigated the associations between various factors anecdotally reported to trigger headache and migraine. Headache symptoms and headache triggers were assessed using a questionnaire given to 180 volunteers. Two groups were identified, those who fulfilled the International Headache Society's criteria for migraine, and those who did not. Associations between reported headache triggers were explored using a principal components analysis, which grouped common headache triggers into four components: visual stimuli, food, alcohol, and stress/tiredness. The visual stimuli cited as triggers included flickering light, repetitive patterns (stripes), sunshine, patterns of light and shade, glare, bright reflections, computers, TV and the cinema. A separate analysis on the data from the migraine group produced the same four components together with a fifth, interpreted as a non-visual sensory trigger (noise and smell). The results demonstrate that visual stimuli are commonly reported as headache triggers. Those involved in the design of the visual environment could improve the quality of life of many by avoiding environmental factors, particularly visual factors, which can trigger headache and migraine.
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  • Michael HIRNING, Steve COYNE, Ian COWLING
    2010 Volume 34 Issue 2 Pages 101-104
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    Daylighting offers environmental, economic and social benefits when applied successfully; however, poor use of daylight causes unwanted heat and glare problems that negate the desired benefits. In order to develop effective daylighting practices, a reliable method for assessing discomfort glare for occupants is required. The aim of this study was to capture the luminance distribution within a daylit scene and use this information to quantify some of the physical parameters of glare. Computational tools were developed that use luminance data from corrected High Dynamic Range (HDR) images captured via a digital camera. These tools then calculate the physical parameters used in glare assessment. The discussed procedures allow for future research into discomfort glare to be informed by real situations, documented by lighting researchers and practitioners. With these tools a better understanding of discomfort glare can be established.
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  • Tse-ming CHUNG, Chun-man KWOK, John MARDALJEVIC
    2010 Volume 34 Issue 2 Pages 105-110
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    Daylight distribution and the associated heat gain of a commercial building with curtain wall façade under different degrees of obstruction are studied. A new metric ‘useful daylight illuminance’ (UDI) is applied to analyze the time varying illuminance distribution on a work plane. The solar irradiance obtained from the daylighting simulation is input to a two-node thermal model for energy simulation. The indoor air temperature profile, cooling and heating load requirement and the associated electrical energy consumption based on a typical coefficient of performance (COP) are reported.
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  • Kazuaki OHKUBO
    2010 Volume 34 Issue 2 Pages 111-122
    Published: 2010
    Released: November 01, 2010
    JOURNALS FREE ACCESS
    The integrating sphere is a useful apparatus for measuring optical radiation. To use or design an integrating sphere for a particular application, it is important to understand how it works in theory. The theory of the integrating sphere is based on the theory of radiation interchange within an enclosure comprised of diffuse reflecting surfaces. In this paper, the theory and error aspects of the integrating sphere are discussed.
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