Lighting is an important component of indoor environmental quality that can affect occupant satisfaction, well-being and productivity. Lighting quality is a broad abstract concept and this has implications for its assessment. Subjective evaluations of lighting are an important complement to objective photometric information; however, there is limited existing guidance for the selection of such measures. We review and highlight the advantages and limitations associated with measures of general lighting quality and discomfort glare. Existing measures of lighting quality have broad coverage of individual lighting features but do not always clearly form cohesive scales measuring an underlying construct. Questions used in experimental glare research focus narrowly on glare severity, with ambiguous response rating scales. There is a need for the development of reliable and valid tools to assess lighting quality and its components, with clearly defined definitions and constructs, and explicit reporting of psychometric scale properties. The development of rigorous self-report tools will improve the understanding and design of quality lighting environments.
Reducing the peak demand for lighting energy through load shedding can be an effective method of load management. However, before such a load-shed technique is applied to the real world, it is important to understand occupants' requirements for the change in illuminance. Two laboratory studies were conducted to better understand occupants' sensitivity and acceptance to dimming-memory study and dimming curve study. The memory study addressed whether one can memorize an initial illuminance level and how long this memory is sustained. The dimming curve study investigated the effects of dimming function on detectability and acceptability of illuminance reduction. Both experiments used a windowless private office illuminated by three dimmable direct/indirect pendant luminaires. After adapting to an initial illuminance of 500 lx, subjects closed their eyes in the memory study while the lighting was dimmed to various illuminance levels. Subjects conducted a paper task or no task (free gaze) in the dimming curve study. The dimming speed and the dimming function varied in the memory study and the dimming curve study respectively. Subjects indicated whether the lighting level had increased, decreased, or remained unchanged and whether the illuminance change was acceptable. Within the range of the experimental conditions, the memory study and the dimming curve study, concluded: 1. Regardless of task, 50 percent of the subjects could detect the change in illuminance after about a 15 percent reduction from the initial illuminance. 2. Regardless of task, 50 and 80 percent of the subjects accepted illuminance reductions up to about 40 and 20 percent respectively. 3. Dimming curvature has no effect on detectability and acceptability of illuminance reduction at slow rates of change.
In this paper the analysis and optimization of a universal high power factor correction circuit for linear fluorescent lamps is presented. The design and analysis criteria for the converter include a universal voltage input, 120 to 277 V AC with power handling capability from no load to 110 watts. In addition a new PSPICE model for universal power factor correction circuit operating in the critical conduction mode has been developed. Simulation and analytical results have been validated against actual laboratory measurements.
The influence of the metal halide mount structure on lamp performance, specifically on sodium loss, was studied. A metal halide mount the so-called structure, was constructed and evaluated. Several types of lamps, including switch-start, pulse-start and phosphor-coated lamps, with this mount construction, consistently demonstrated improved lumen maintenance and reduced lamp voltage rise over life. Color shift was also lessened compared to that of control lamps. An accelerated life test using a vacuum outer envelope confirmed the reduced sodium diffusion for the strapless structure. Spectroscopic measurements and wet chemical analysis revealed less sodium loss, lower iodine pressure and more stable ratio between scandium and sodium emissions for the lamps with the strapless structure. The mechanism for the enhanced performance of the strapless structure is discussed in the paper. It was determined that the strapless structure reduces photoelectron emission and thus retards sodium diffusion through quartz. Elimination of the electrically conductive metal straps is the main contributor to the improved performance. In addition, the procedures for an accelerated life test and spectroscopic analysis on sodium loss are described in the paper.
Forty participants viewed a series of greyscale images of a typical non-daylit, open-plan partitioned office, and rated them for attractiveness. The image was projected onto a screen at realistic luminances and 54 percentof full size. The images in the series were geometrically identical, but the luminances of important surfaces were independently manipulated. Initially, the combinations of luminances were random, but as the session continued, a genetic algorithm was used to generate new images that generally retained features of prior images that were rated most highly. As a result, the images presented converged on an individual's preferred combination of luminances. The results demonstrated that this technique was effective in reaching a participant's preferred combination of luminances. There were significant differences in room appearance ratings of the most attractive image compared to other images, and the differences were in the expected direction. Factor analysis of ratings of the most attractive images revealed a factor structure with some similarity to that obtained when people rated real office spaces. Furthermore, preferred luminances were similar to those chosen by people in real settings, as was the variation in preferences between individuals. Finally, subjective ratings of brightness, uniformity and attractiveness were significantly related to luminances in the image.
From January 2001 all lighting products on the European market had to be IEC 61000-3-2 compliant. The IEC 61000-3-2 standard sets limits on the 3rd and 5th harmonic input current as well as the conduction angles. Low power lighting products were not initially compliant to the new standard because the value of the DC bus capacitor was too high. Choosing a very low capacitor value is not advisable as it increases the lamp current crest factor and reduces the life of the product. Therefore, selection of the capacitor value is a trade off between the lamp current crest factor and the level of input current distortion. This paper presents two simple mathematical tools to determine the capacitor value to meet the IEC 61000-3-2 specifications and to predict the performance of the CFL lamp for a given input voltage and lamp power. Based on mathematical modeling, two mathematical tools have been developed. The first mathematical tool determines the maximum capacitor value that satisfies IEC 61000-3-2 requirement for low power lighting products. Based on the capacitor value selected by the first mathematical tool, the second mathematical tool determines the magnitudes of the third and fifth harmonic in the input current, conduction angles, power factor, THD and a DC bus crest factor. The two mathematical tools proposed in this paper are the simplest and cheapest ways to meet the IEC 61000-3-2 standard and predict the performance of the lamp. More important the proposed tool can be widely used for all low power lighting products in the countries where IEC 61000-3-2 has not yet been introduced. By using the proposed method the cost of an electronic ballast is reduced and the power quality significantly improved. By reducing the capacitor value, the lamp current crest factor is slightly increased but it is still acceptable for CFLs. Results obtained from the proposed mathematical tools have been validated with experimental results for 9, 15 and 23 W lamps.
Gilberto J. C. da Costa and Joel L. Cuello The normalized quantum efficiency (RQE) curve that shows the relative photosynthetic response to light of the average photosynthesizing plant was used as the basis in developing the phytometric system, a new concept of light measurement for plants. Based on the multiplication of the RQE curve with the spectral power distribution (SPD) of a given light source, the phytometric measurement would yield units of phytoW.m - 2 . The unit phytoW easily provided conversion factors to the radiometric, photometric, and photon flux (quantum) systems within the photosynthetically active radiation (PAR) of 400 to 700 nm or within the extended PAR of 300 to 800 nm. The use of the phytometric system was demonstrated by applying it to four types of high-intensity discharge (HID) lamp. Pertinent conversion factors were calculated for each lamp type.
This paper provides an algebraic expression that predicts the tabulated values of the V(λ) function with very high accuracy. The model is a linear combination of four Gaussian functions. This concise presentation of V(λ) appreciably simplifies computational applications in such fields as illuminating engineering, photometry, and vision science.
Current luminaire photometry is relied on using the rotating-mirror or the rotating-detector photometers. While these photometers offer great flexibility and speed in acquiring intensity data in the field around the luminaire, the fact that they use a predefined detector-distance with a fixed incident-angle has demonstrated to be a constraint for the real world applications. The paper presents a new design concept of photometric data acquisition system, Linear Moving-Detector Photometer. This photometry methodology performs the intensity measurements at various distances and at different incident-angles relative to the luminaire in three-dimensional space by using a computer controlled moving-detector system. The photo-detector travels a wide range of distances from a few inches to many feet in a three-dimensional field surrounding the luminaire. It then acquires photometry at the desired locations and orientations. For a typical application, thousands of measurement data can be collected and stored in the computer database. This allows luminous flux and intensity to be reported in both spherical and Cartesian coordinate systems as are required by the specific lighting applications. Actual illuminance distribution on any surfaces in this photometric field can be generated. While linear moving-detector photometer system was not developed to replace existing photometry equipment, this automated equipment will supplement and enhance current photometry methodology.
Video-conferencing is a fast growing tool for communication and education. Proper lighting is vital to the success of communication through video-conferencing, but it is seldom provided. Past recommendations for lighting these complex spaces have been based on laboratory research and practical application investigations of respected researchers and designers. However, verification of these techniques in field studies has not been reported. This paper documents a recently completed field study testing user preference for several lighting approaches in a two-way interactive distance-learning classroom. The experiment was designed to measure students' and instructors' lighting preferences in a video-conferencing setting at a local community college with an established distance-learning program. Three different lighting distributions and two background conditions were evaluated during instructional periods of the fall 2000 academic semester. The lighting approaches included direct lighting, completely indirect lighting, and direct/indirect lighting with maximum lumen output at a 45 degree angle. Local and remote participants evaluated the general lighting of the classroom, their ability to perform typical tasks, and the appearance of students and instructors. Results show that instructor-selected lighting levels were generally lower than those recommended by earlier guidelines. Statistical analyses show several statistically significant responses to the different conditions. Wholly indirect lighting was preferred by all participants for a wide range of variables and conditions. Direct/indirect lighting, although liked by the students, was not preferred by the instructors. Direct lighting was least preferred. This research clearly establishes user lighting preferences, supports these preferences with physical explanations, and offers preliminary guidelines for similar applications.
The Absolute Integrating Sphere Method is now used at NIST for the detector-based calibration of total luminous flux of lamps, as well as for the realization of the lumen. This method has many benefits, allowing for measurement of total luminous flux in reference to an illuminance standard photometer, not requiring use of total luminous flux standard lamps, thus eliminating uncertainties associated with the transfer process and aging of the working standard lamps. This method however, requires absolute calibration of many components of the sphere system and is liable to errors if not performed correctly and thus, not generally recommended for industrial laboratories. To overcome this difficulty, a simplified, new approach for industrial use of this method is proposed. An integrating sphere system of the same design as that of NIST can be initially calibrated against luminous flux reference standard lamps, with no need for characterization of all the parameters required for the absolute sphere method and allows for the detector-based measurement of test lamps with all the benefits to achieve lower uncertainties. The principles and procedures for this approach are presented.
This paper reports on a computer modeling study to assess the performance of different photosensor-controlled diming systems in a daylighted classroom space. The study addresses different photosensor spatial response functions, ceiling positions relative to the window wall and control algorithms. The results show that each of these features impacts overall performance. In particular, the view that each of these features impacts overall performance. In particular, the view that the photosensor has of the window is inversely related to its ability to properly track the daylight provided and dim the electric lighting system accordingly.
In previous work, the metrics of Unit Power Density (UPD) and Unit Uplight Density (UUD) were applied to roadway lighting systems, demonstrating the significance of evaluating the performance of entire lighting systems instead of individual components. Using that work as a baseline, this paper evaluates the relationships between system uplight-measured by UUD-and UPD, intensity-based classification, uplight percentage and uplight classification.The optimized roadway lighting systems reported in previous work were used as the basis for UUD calculations for those luminaires with complete photometry. The correlation between UPD and UUD is reported both overall and for the sub-domains of wattage and number of lanes, for both HPS and MH sources. The portion of uplight calculated from the luminaire's photometry is the basis for an additional set of correlations. The relationships between uplight and luminaire classifications are investigated, with separate consideration of intensity-based and uplight-based classifications.Results show significant correlations between UPD and UUD. This applies overall and within almost all sub-domains. Correlations between UUD and intensity-based classification are mostly significant but inconsistent. Correlations between UUD and the luminaire's uplight are mostly significant and quite strong but also inconsistent. There are small and expected reductions in the strength of correlations when the uplight data is fitted into a proposed uplight classification.Conclusions include that a roadway lighting system's uplight corresponds closely to both system UPD and luminaire uplight, but not as strongly to the intensity-based classification. The proposed classification based on luminaire uplight appears to be informative.
This paper presents an efficient analytical procedure for the exact substitution of an extended ideally diffuse light source (IDLS) with only one point light source in the near-field zone. Different IDLS geometries are considered and example illuminance calculations (horizontal, vertical and vector/magnitude) for a rectangular IDLS are performed. Some aspects of the proposed procedure are considered in terms of photometric measurements and practical applications.
In today's High Intensity Discharge (HID) marketplace, there is a high demand for electronic ballasts that are compact, lightweight, efficient and reliable. Customers are requesting information regarding lamp-ballast compatibility and asking the question to lamp and ballast manufacturers: "Will this lamp work with this ballast"?" Lamp and ballast manufacturing companies have been investigating and discussing, at ANSI meetings, test methods for verifying the compatibility of lamps with electronic ballasts. A focus of this paper is on lamp-electronic ballast compatibility testing with ceramic discharge metal halide lamps that are used in applications ranging from specialty store lighting to gas station canopy lighting.Testing guidelines are discussed in this paper for low frequency,(LF) electronic ballasts as well as LF electronic ballast characteristics and observed failure modes. An acceptable electronic ballast will show lamp performance with test ballasts as good as or better than lamps operated with corresponding ANSI compliant magnetic ballasts. This paper concludes with guidelines of general ballast specifications for "good" LF electronic ballast designs that testing has shown will provide long lamp life.
The key features of MR16 halogen reflector lamps include their small size, color temperature, color rendering, variety of wattage and beam spreads, durability and ease of maintenance. These lamps are very attractive for retail and residential lighting applications. Currently, manufacturers provide optical information that includes only center beam candlepower and beam spread, with no mention of beam pattern uniformity, which is very important to specifiers. Typically, users must rely on experience or perform mockup studies to identify a desired beam pattern and to check beam quality. The latter is especially time consuming and expensive. A beam quality metric would not only aid lighting specifiers in differentiating good product from bad, but would also help manufacturers improve beam quality. Several researchers have previously attempted to quantify beam uniformity with limited success, since perceived beam quality depends on several factors including distance of the lamp to the target, distance of the observer to the target, background illuminance and target pattern and color. The present study analyzes and modifies a beam image captured by a CCD (charge-coupled device) camera, translating these data into a perceptual beam image. This processed image is used quantify beam quality by Summing the deviations caused by nonuniformity in the beam. This process was employed to obtain a metric rating of several MR16 lamps. In a separate experiment, human subjects indicated their preference for each beam through a series of paired comparisons.. The ratings obtained from the image analysis compared well with those obtained from the human subject evaluation.
In this paper, we examine the operation of a low-cost, high-power factor electrolytic-less ballast. A new mathematical model has been developed to analyze the operation of the electronic ballast when the electrolytic DC bus capacitor is eliminated. The primary application of this ballast is for compact fluorescent lamps. The lamp efficiency, life and light modulation are going to be the same as for ballasts that operate the lamp at the power line frequency. Theoretical and experimental results prove the electrolytic-less ballast achieves a high power factor without the inclusion of high power factor correction circuits. This significantly reduces the cost, size as well as the complexity of the electronic ballast. Simulation and experimental results are provided to verify the results obtained by using the proposed mathematical model.
Several studies show that the surround conditions of an on-axis target have a significant effect on target visibility at the threshold between the target and the surround. In complex visual fields such as roadways in urban areas, where a target signal-to-noise ratio is often low, the surround conditions of targets may significantly impair a driver's ability to detect the targets.This study investigated how the immediate background size of an off-axis target influences a driver's detection of the target at a mesopic light level under different conditions. The experiment used a target (subtended 2 ? 2 degrees) framed by a square-shaped immediate background surrounding the target, and framed by a larger square-shaped far background surrounding the immediate background. The experiment varied the luminance contrast of the target to the immediate background and the size of the immediate background, but kept the luminance of the far background constant at 0.009cd/m(2). The target was located at 15 degrees off-axis and was presented to six subjects under each condition. The reaction times and number of missed trials of detecting targets were measured to evaluate the subjects' ability to detect a change in the luminance contrast. The results suggested that, if the width of the immediate background framing the target was narrower than the size of the target (2 degrees), the immediate background impaired the subjects' peripheral detection of targets at the threshold. When the width of the immediate background was wider than that of the target, the reaction time was constant regardless of the width of the immediate background. As these results show, conventional luminance contrast of a target to its background cannot take into account the spatial effect of a complex luminance distribution around a target on the detection of the target. To quantitatively investigate how the immediate background influences the target detection, this study attempted to adopt an image filtering method developed by Nakamura that can analyze how strong and how frequent luminance changes exist over a specific area and its surrounds. The results of the analysis suggested that this image filtering method could explain the mechanism of target detection under complex background conditions.
