Illuminance Ratio Research Articles

Contrast ratios and masking ability of three types of ceramic veneers

Although ceramic veneers have been proven to be clinically successful in longevity studies, there is little information on the contrast ratios and masking ability of the available ceramic systems because dental laboratory technology and expensive experimental equipment are required for the investigation. Moreover, the complexity in understanding how to evaluate translucent ceramic materials may also explain why information in this area is limited. The purpose of this study was to determine the contrast ratios and masking abilities of 3 types of all-ceramic veneers by measuring their luminance and color difference over white and black backgrounds. Disk-shaped specimens (8-mm diameter x 0.7-mm thickness) of Shade A2 (Vita Lumin) of 3 types of all-ceramic systems: Procera (n=8), Empress 2 (n=8), and Vitadur Alpha (n=10) were fabricated. The luminance (as Y) and color (as CIE L*a*b*) of the specimens were measured with a colorimeter. The contrast ratio (CR=Yb/Yw), defined as the ratio of illuminance (Y) of the test material when it is placed on the black background (Yb) to the illuminance of the same material when it is placed over a white background (Yw), was determined. The masking ability of a specimen was evaluated by calculating the color difference (DeltaE) of the veneers over white and black backgrounds. Both CR and DeltaE* data were analyzed with 1-way ANOVA and the Tukey HSD test (alpha=.05). The mean contrast ratios (SD) of Procera, Empress 2, and Vitadur Alpha specimens were 0.50 (0.02), 0.46 (0.05), and 0.39 (0.02), respectively. CR values were significantly different among the 3 materials (P<.001). Procera veneers had a significantly higher CR compared to Empress 2 (P=.01) or Vitadur Alpha (P=.01), whereas the CR of Empress 2 was significantly higher than that of Vitadur Alpha (P=.046). Color difference (DeltaE*) (SD) of Procera, Empress 2, and Vitadur Alpha specimens over black and white backgrounds were 24.46 (1.03), 25.80 (1.03), and 31.08 (1.19), respectively. DeltaE* values were statistically different among the 3 materials (P<.001). Vitadur Alpha specimens had significantly higher DeltaE* when compared with Procera (P<.001) or Empress 2 (P<.001), whereas DeltaE* values between Procera and Empress 2 were not significantly different (P=.331). Vitadur Alpha had significantly lower contrast ratio and poorer masking ability compared to Procera or Empress 2. The clinical application of Vitadur Alpha as a veneer material over discolored teeth is cautioned. Although the contrast ratio of Procera was significantly higher than that of Empress 2, the masking abilities of these materials were not significantly different. The clinical application of these 2 ceramics as a veneer material may still be limited when applied over intense tooth discoloration because neither can fully mask the color of a black background.

New method for specifying color‐rendering properties of light sources based on feeling of contrast

Abstract“Visual clarity” or “feeling of contrast” of object colors under illumination is affected significantly by changing color‐rendering property of light source used. Though the feeling of contrast is considered one of the most important characteristics on color‐rendering properties of light sources, it cannot be estimated adequately by using the present Ra method. The new index FCI is proposed for estimating the effect of feeling of contrast quantitatively under any light sources. The FCI is derived using a simple transformation of the gamut area, which is constituted by a specially selected four‐color combination in CIE LAB color space. The FCI correlates well with the illuminance ratio for equal feeling of contrast (or equal visual clarity) on various light sources reported so far. Using the FCI together with the present CIE Ra, the color‐rendering capability of a light source can be well clarified. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 361–371, 2007

Monitoring of a light-pipe system

Natural light is an important element in visual comfort and it sometimes influences the quality of vision. The effect of daylight on the human biological cycles and possible physiological alterations in the absence of natural light during the day are well-known. When visual comfort is not completely satisfied, the application of daylight transportation systems in buildings is relevant. Research on and observation of human behaviour and the biological effects of light have shown the vital role of artificial or natural light, in maintaining the physiological and psychological balance in human organisms. When visual comfort is not completely satisfied the constant use of artificial light cannot give a temporal reference, so a careful design of the building as well as the use of a specific daylight component (to control, capture and distribute daylight) that contributes to maintaining the natural light changes in intensity and colour temperature is necessary. Several prototypes have been developed and experience has been obtained in daylight collection and transportation; for example, the light-pipes that represent simple systems to capture and transport the natural light inside a room. Light-pipes (such as tubular light) are simple structures that allow the transmission of daylight from the outside to the inside of a room. They are realized with a top collector (often just a polycarbonate hemispheric dome), the pipe itself, and an emitter. Light-pipes have different designs and they are constantly being improved and updated. The pipes that we intend to analyse have a reflective aluminium sheet with a reflectance of about 99% that transmits the light through multiple specular reflections and that makes the light-pipe increasingly efficient. This paper presents the results of monitoring a light-pipe located inside a windowless laboratory of about 9 m 2. The system has been monitored with a luxmeter to evaluate the distribution of the illuminance on a working-plane from January 2005 to June 2006. The indoor and outdoor illuminance and the internal/external illuminance ratio are shown in the graphs.

Visual Adaptation to Interocular Brightness Differences Induced by Neutral-Density Filters

Interocular brightness differences such as those caused by asymmetrical cataract have been found to have a minimal effect on interocular brightness matches. In the present study, the measured binocular visual response to interocular differences in retinal illuminance was measured over time. Interocular differences in retinal illuminance of magnitudes 0.3, 0.6, and 0.9 log units were induced using neutral density (ND) filters under two conditions: (1) naturally mobile pupils and (2) with fixed artificial pupils (3 mm). Interocular brightness differences were quantified by measuring interocular brightness matches using the simultaneous interocular brightness sense test every 15 minutes over a 2-hour period in eight visually normal subjects. Initial interocular brightness matches were as predicted by the induced interocular differences in retinal illuminance (P > 0.05). A significant reduction in the interocular difference in brightness was observed over time (P < 0.01). These reductions in the interocular difference in brightness over time followed a logarithmic progression reaching asymptotic values equal to the reciprocal of the square root of the interocular retinal illuminance ratio. This value is equal to the midpoint of the induced interocular difference in retinal illuminance at time 0 and that found without the introduction of the ND filters. Binocular visual adaptation to interocular brightness differences occurred with both mobile and fixed pupils. Visual adaptation occurs in response to interocular brightness differences induced by asymmetrical ND filters. The level of visual adaptation can be predicted by Fechner's Paradox and is independent of interocular differences in pupil diameter.

Could Daylight Glare Be Defined Mathematically? Results of Testing the DGIN Method in Japan

Discomfort glare from daylight is a common problem without valid prediction methods so far. A new mathematical DGIN (New Daylight Glare Index) method tries to respond the challenge. This paper reports on experiments carried out in daylit office environment in Japan to test applicability of the method. Slight positive correlation was found between the DGIN and the subjective evaluation. Additionally, a high Ladaptation value together with the small ratio of Lwindow to Ladaptation was obviously experienced sufficient to neutralize the effect of glare discomfort. However, subjective assessments are poor glare indicators and not reliable in testing glare prediction methods. DGIN is a good indicator of daylight glare, and when the DGIN value is analyzed together with the measured illuminance ratios, discomfort glare from daylight can be analyzed in a quantitative manner. The DGIN method could serve architects and lighting designers in testing daylighting systems, and also guide the action of daylight responsive lighting controls.

An Analysis of Nonovercast Sky Luminance Models Against Hong Kong Data

Daylighting is an important issue in modern architecture that has been characterized by the use of curtain walls in buildings. Nonovercast skies, including clear and partly cloudy days, are essential because they may occur more frequently for places such as in equatorial regions and the tropics. Better understanding of nonovercast sky luminance distribution is vital to estimate the dynamic variation in daylight illuminance as sky condition and solar position change. This paper presents the work on the evaluation of six clear sky and three partly cloudy sky models against three-year (1999–2001) measured Hong Kong sky luminance data. The general features and characteristics for the models were described and assessed. The nonovercast sky conditions were identified using the ratio of zenith luminance (Lz) to diffuse illuminance (Dv) and the ratio of global illuminance (Gv) to the extraterrestrial illuminance (Ev). Subsequent interpretations of the clear skies into high and low turbid types were conducted in conjunction with the cloud cover (CLD) and the luminous turbidity (Tv), and partly cloudy skies were further subdivided into thin and thick cloud modes using sunshine hour (SH) and global irradiance (GSI). A statistical analysis of the models revealed that the Gusev model (i.e., CIE (Internal Commission on Illumination) polluted sky No. 13) and the model by Chen et al. (1999, “Luminance Distribution Model of Intermediate Skies,” Zhaom Ing Gong Chen Xuebao, 10(1), pp. 59–63 (in Chinese)) developed using artificial neural network (ANN) theory with the measured data in Chongqing, China (29.6degN and 106.5degE) showed the best predictions for sky luminance at this location under the clear and partly cloudy sky conditions, respectively.

Predictive tools for evaluating daylighting performance of light pipes

This study describes the methods of predicting light pipe performances using scale models under the tropical Malaysian sky conditions. The conversion factor is introduced as an indication of the reliability of the methodology employed in predicting the light pipe performance. Illumination ratios were analysed and empirical model equations were developed from simultaneous measurements of interior and external illuminances. The model equations derived from this study could hopefully be adopted for other types of light pipe materials or other applications related to light pipe technologies. Copyright , Manchester University Press.

Daylight performance of anidolic ceiling under different sky conditions

The daylight performance of anidolic ceiling for diffuse daylight is the subject of this article. The performance is assessed over a wide range of sky conditions following the new CIE Standard General Sky and compared between locations in Singapore, Japan and the United Kingdom. The criteria illuminance ratio (IR) and daylight glare index (DGI) are used to quantify the daylight performance of a default ribbon window façade with and without an anidolic ceiling. The difference is expressed in new terms IR improvement factor (IR IF) and DGI reduction. These factors are charted over all 15 sky conditions and various sun altitudes and may serve as general references indicating conditions under which anidolic ceilings perform best. The application of these new terms are demonstrated for Singapore, Fukuoka and Sheffield, representing three main latitude bands and different sets of prevailing sky types. It can be concluded that the daylight performance improvement through anidolic ceilings is most significant in Singapore.

On the Relationship between Object Modeling and the Subjective Response

This paper summarizes exploratory research that is a first step toward objectively linking the three-dimensional light-field associated with object modeling to occupants' subjective impressions of a space. Computer models were created for six light settings studied by John Flynn for which he determined specific subjective impressions. The directional nature of the light-field was quantified for each light setting using a three-dimensional array of vector to scalar (V:S) illuminance ratios, which have been promoted by Christopher Cuttle as a method for characterizing three-dimensional modeling. The comparative analysis suggests that: 1) spaces with variation in the V:S ratio are preferred to spaces that have homogeneous ratios, 2) the combination of a lower V:S ratio (less than 1.2) coupled with low variance in the V:S ratio favors spaces that appear spacious, and 3) impressions of clarity may be related to a combination of the V:S ratio and illuminance.

A comparison of visual objectives used in side-by-side matching tests

This paper compares the different visual objectives that have been used in side-by-side matching experiments. In tests, two different fluorescent lamps were compared in juxtaposed booths by a series of observers. It was found that:(i) there was no significant difference in illuminance ratio when matching the booths according to six different visual objectives including equal brightness, equal clarity and equal pleasantness; and (ii) the matched condition was not predicted by illuminance based on V(l). The data exhibited the error associated with the application of dimming previously noted by Fotios.

Comparison between winter and summer sky-luminance distribution in Central Europe and in the Eastern Mediterranean

This work studies the illuminance levels at a city in Central Europe (Bratislava) and another in the Eastern Mediterranean (Athens) and defines the prevailing sky-luminance distributions for winter and summer. The data used are 5-min values of global and diffuse horizontal irradiance and illuminance along with zenith luminance from the IDMP stations at the two cities for a period of 5 years. The study is based on the new set of the sky types recently adopted by CIE. These sky standards correspond to 15 theoretical diagrams of the ratio of zenith luminance to diffuse horizontal illuminance against solar altitude. The theoretical curves converge above 35 ∘ of solar elevation and in many cases they intersect each other. For this reason, each observation is classified into one of the 15 sky standards, only when the value of the ratio of zenith luminance to diffuse horizontal illuminance lies in a zone of ± 2.5 % around the theoretical curve describing the specific category. If any observation is classified into more than one sky standards, the corresponding ratio of global horizontal illuminance to extraterrestrial horizontal illuminance is compared to the average ratio of the sky types implicated, for the same solar altitude, and the observation is classified in the sky type with the nearest value. It is found that the most frequent sky types for Bratislava are the overcast sky with steep luminance gradation and slight brightening towards the sun (winter) and the white–blue sky with a distinct solar corona (summer), while for Athens the cloudless polluted sky prevails in both seasons. It is also found that during a summer day, a noticeable shift appears in the sky-luminance distribution at both sites.

A Basic Study on the Prediction of Luminous Intensity Distribution Curves of the Light Source Using the Floor Illuminance Distribution in a Room

We have already published several papers describing application of an approximate calculation method for calculating interreflection in a room with fixtures. As a result, it is clarified that the illuminance ratio (illuminance ratio =the floor illuminance in a room with fixtures / the floor illuminance in a room where fixtures do not exist) distribution on the floor does not depend to the luminous intensity distribution curves of the light source. The method is presented for predicting the floor illuminance in a room (we called this the real space) with fixtures and a non-uniform diffuse light source from the floor illuminance in a room (we called this the virtual space) with no fixtures. In the previous paper, we presented that the luminous intensity distribution curves of light source of the narrow angle type and wide angle type can be represented as a polynomial expression with the components of cosine to the kth power and angle ακ of maximum luminous intensity. This paper proposed a method for predicting luminous intensity distribution curves of the light source when desired floor illuminance distributions is given. (we called this the inverse problem) This inverse problem of lighting design is useful for designing practical rooms, and ito procedures are as follows. First, the floor illuminance distribution of real space is replaced with floor illuminance distribution of virtual pace. Next, the relationship between position of the floor and floor illuminance distribution in a virtual room is expressed by the sixth equation. Finally, the relationship between the coefficient of the sixth polynomical with degree κ and the angle ακ of maximum luminous intensity of the light source is discussed. As a result, it is clarified that the luminous intensity distribution curves of the light source could be predicted from the coefficient of the equation, which has relation to floor illuminance distribution.

見かけの明暗割合を考慮した人の顔のモデリング評価 : 窓際での人の顔のモデリングに関する研究 その5

In the former study by the authors the boundary position (angle) of light and shade areas perceived on the cylinder surface was consistent with that showing the largest ratio of luminance (or illuminace) at successive two points on the cylinder surface. The apparent proportion of light and shade areas of the face was geometrically obtained by the boundary position (angle) of the light and shade areas when the face was simulated as a half cylinder and satisfactorily explained the perceived modeling. In the present study the data obtained in the previous experiments on the modelling evaluation was synthetically analyzed. As a result a multiple regression model for modelling of human face at a window was constructed with two variables of the semi-cylindrical illuminance ratio and the apparent proportion of light and shade areas.

A 1/3'' VGA linear wide dynamic range CMOS image sensor implementing a predictive multiple sampling algorithm with overlapping integration intervals

Many tasks performed by machine vision systems involve processing of natural scenes with large intra-frame illumination ratios. Thus, wide dynamic range visible spectrum image sensors are required to achieve adequate processing performance and reliability. An image sensor implementing an algorithm that linearly increases the illumination dynamic range of solid-state pixels is presented. Optimal exposure is achieved with a predictive pixel saturation decision that allows for multiple integration intervals of different duration to run concurrently for different pixels while keeping the sensor frame rate constant. A proof-of-concept chip was fabricated in a 0.18-/spl mu/m CMOS process. Added functionality to standard imagers is mainly concentrated off-pixel so fill factor is not sacrificed. Measured data corroborates the algorithm functionality.

Classification of daylight and radiation data into three sky conditions by cloud ratio and sunshine duration

An analysis of daylight and solar radiation data in low latitude/tropics area has been done. This analysis classified three sky conditions: clear sky, intermediate sky and overcast sky. There are two methods have been used to classify these sky conditions. Firstly, cloud ratio method that is the ratio of the diffuse illuminance or irradiance to the global illuminance or irradiance. This method based on data measured at the IDMP Station at Hasanuddin University during 1995–2000. Another method is sunshine duration, which is based on the data measured at meteorological observatory in Makassar during 1995–2000. This study aims to investigate the accuracy of daylight and solar radiation data gathered during 1995–2000 by comparing data measured from two different sources above. The results of both methods are relatively similar, which indicate that daylight and solar radiation data gathered in Makassar are accurate and useful for various daylight designs and applications.

A model for calculating global illuminance from satellite data

A model for calculating global illuminance on horizontal surfaces from meteorological satellite data was developed. The data used for developing the model are global illuminance measured at four solar monitoring stations situated in different parts of Thailand and 8-bit digital data from visible channel of GMS-5 satellite covering the whole country for the period of 1–2 years. Values of normalized global illuminance defined as a ratio of global illuminance to clear sky global illuminance were calculated. These values were used to correlate with those of cloud index derived from the satellite data. From the correlation, a model relating the normalized global illuminance to cloud index was established. The performance of this model was investigated using an independent illuminance data set. It was found that the global illuminance calculated from the model agreed well with that obtained from the measurement, with a root mean square difference of 5.38 klux or 7.0% of the mean values.

Lighting controls in areas with innovative daylighting systems: a study of sensor type

Innovative daylighting systems often work by redirecting light from the sky and sun onto the ceiling from where it is diffused to light the space. This can cause problems for ceiling mounted photoelectric control sensors. The performances of three types of ceiling sensor were studied in the Building Research Establishment’s mock-up rooms. The window systems included venetian blinds, prismatic film and a light shelf as well as ordinary clear glass. A completely unshielded sensor gave surprisingly stable performance compared with horizontal working plane illuminance. The main exception to this was when direct sunlight reached the sensor itself. Unfortunately the ratio of sensor illuminance to horizontal illuminance was significantly greater under sunny skies than under overcast skies. This could lead to uneven control performance under different sky conditions. An alternative sensor shielded by a darkened tube was also tested. This proved to be very susceptible to the location of patches of sunlight in the space. In a real room it could also be affected by the positions and reflectances of furniture and even occupants. A possible compromise is the use of a partially shielded sensor. This can receive light from all directions except the window. Care is needed in aligning the shield correctly during installation.

Reasonable Lighting Factors for Work Environment with VDT Tasks

This paper presents a proposal to design factors for a reasonable lighting environment in Visual Display Terminal (VDT) work, by monitoring changes in the lighting environment by general illumination and partial illumination as a factor of the working environment. We also considered that this factor affects productively and workload from an experimental approach. Since we think that it is not enough to evaluate a lighting environment only by subjective appraisal, we used brain waves as a physiological index for evaluating human mental activity objectively. The evaluation index used in the experiment were obtained by measuring working efficiency and working quality in VDT work, mental changes (stability) recorded by an electroencephalograph (EEG), and determined the workload by a survey of subjective symptoms and by measuring eye fatigue. The results enable us to derive a relationship between reasonable lighting environment and illuminance. The results show the following: 1)When the partial illumination was given to subjects, it was shown to effect their concentration on work and mentally stabilize at the ratio of surround illuminannce to horizontal illuminance was about 0.05. 2)When the ratio of surround illuminance to horizontal illuminance was the same, the effect showed remarkable at the ratio of vertical illuminance to horizontal illuminance was lower.

A Study on the Practical Use of a Task and Ambient Lighting System in an Office.

The possibility of the practical use as an office lighting system, which make the total illuminance of 400lx and Task and Ambient illuminance ratio of 1.0 on the working desk, by using Task and Ambient Lighting system was reported on the last year research. On this year research, the following aspects were indicated based on the analysis of the psychological queries after two weeks actual work in the specific illuminance level and Task and Ambient illuminance ratio. The illuminance level of 200lx on a working desk cause some psychological problem as room and desk area ‘darkness’ and illuminance level ‘unevenness’. These problems were improved when the illuminance level of 300lx was applied. And this analysis suggested that the Task and Ambient illuminance ratio shall be around 1.0. An approximately 20% saving energy can be achieved under this lighting system condition compared with the general office lighting system.

Enhancement of crop illuminance in high latitude greenhouses with laser-cut panel glazing

This paper presents theoretical predictions and experimental measurements of the enhanced illuminance available in high latitude greenhouses in winter by use of double-glazing comprising laser-cut panels and glass to deflect low elevation sunlight onto the crop. Provided the structure of the greenhouse is optimised for light enhancement, i.e, single slope south-facing roof with vertical north wall, the predicted daily time averaged enhancement, the ratio of horizontal illuminance with laser-cut panel double-glazing to that obtained with a single clear glazing, approaches 100% for most of winter in greenhouses at latitudes >50°; much greater than the enhancement that can be achieved with other passive optical systems investigated. The predicted enhancements, which take account of diffuse sky and direct sunlight components, are strongly dependent on latitude and atmospheric turbidity and agree with experimental enhancements measured in scale model greenhouses.