Showing papers in "Lighting Research & Technology in 2010"

The performance of occupancy-based lighting control systems: A review

Abstract: This paper reviews the literature on occupancy-based lighting control as a prelude to the application of sensor networks to building management. Many buildings include systems to detect occupancy and control building services. Current systems use single measurement points to detect occupancy, and there can be significant uncertainty associated with the measurement of occupancy. Long time delay and high detector sensitivity settings compensate for this uncertainty, but these diminish the savings that could be achieved with more accurate occupancy measurement. More effective control may be provided by more extensive sensing, using a network of occupancy sensors, and more extensive analysis of sensor data. The literature reviewed in this paper establishes the need for an investigation of the performance of sensor networks when used for lighting control.

Effects of dynamic lighting on office workers: First results of a field study with monthly alternating settings

Abstract: Dynamic lighting is designed to have positive effects on well-being and performance. In a field experiment we tested whether these effects are detectable and stable over time when employed in actual work settings. The study consists of two tranches, one following a monthly alternating experimental design, the other a yearly alternating one. This paper reports on the first tranche. In a dual balanced design, office workers experienced dynamic or static lighting according to an a-b-a /b-a-b scheme over three consecutive periods (N = 142, 90, 83). Questionnaire data suggest no significant differences for need for recovery, vitality, alertness, headache and eyestrain, mental health, sleep quality, or subjective performance, although employees were more satisfied with the dynamic lighting. Implications and limitations of the study are discussed.

Lighting in retail environments: Atmosphere perception in the real world:

Abstract: Although ambient lighting and atmosphere are intuitively related, there is a paucity of empirical, naturalistic data supporting such a relation. The objective of this study was to investigate the contribution of lighting in evoking an atmosphere in the real world, amongst the extensive set of other cues available there. In a field study involving 57 clothing stores, lighting attributes (e.g. brightness, contrast, glare and sparkle) and context (i.e. the shop’s interior) were assessed and quantified independently. These data were then used to predict four dimensions of perceived atmosphere in hierarchical regression analyses. Lighting attributes and interior qualities were both related to perceived atmosphere. This indicated that, even given the substantial contribution of design elements in retail environments, lighting plays a role in evoking atmosphere.

Towards the third stage of the lighting profession

Abstract: The notion of stages of the lighting profession is examined to identify the main themes that have directed the objectives of the lighting profession. It is proposed that the objective of the first stage was provision of uniform illumination over a horizontal plane, and that of the second stage has been to provide illuminance suited to human need, based on visual performance. This brings us up to the current era, and it is the author's opinion that the second stage has failed to achieve its objective. While codes and standards pay lip service to visual performance, the reality is that for the vast majority of situations where lighting standards are applied, the aim is to meet user expectations for the spaces they occupy to appear adequately lit. The metrics currently used to specify, measure, and calculate lighting levels are inappropriate for this purpose. The concept of mean room surface exitance is proposed as a basis for lighting standards. Procedures for calculation and measurement lead to some startling conclusions. Familiar notions of lighting effectiveness and efficiency are turned upside down, and an entirely different way of thinking about interior lighting design is revealed. The essential difference is a switch from assessing light incident on planes to assessing light arriving at the eye. Such a change of thinking may be seen as a precursor for the third stage of the lighting profession.

Office workers’ daily exposure to light and its influence on sleep quality and mood:

Abstract: To study the amount of light entering the eye and its effects on office workers, measurements were taken from 23 office workers over a period of seven consecutive days. Two parameters of visible light were recorded: (i) illuminance and (ii) irradiance of the blue spectral component. Every evening before going to bed, a questionnaire had to be filled out, containing scales relating to the mood dimensions of pleasure and arousal, questions about the previous night’s sleep and a rough time table with information about the person’s whereabouts during the day. The exposure to light on workdays is regular but it varies strongly on days off. No evidence could be provided for the influence of age, sex or seasonal affective disorder (SAD) scores on the daily exposure to light of office workers. The amount of light entering the eye during the day appears to have a positive impact on sleep quality the following night. Pleasure and arousal were not significantly associated with daily light exposure.

Field surveys of the effect of lamp spectrum on the perception of safety and comfort at night

Abstract: Public lighting improves visibility and provides orientation. It also contributes to the perception of comfort and safety of people outside after dark. At present, highpressure sodium lamps are widely used in street lighting. This is in part due to their high efficacy and relatively long lifetime (≥16 000 hours). Their use, however, comes at the expense of good colour rendering. Recently developed ceramic metal halide lamps provide many of the advantages of HPS in addition to white light and better rendering of colours. In this paper, results of research conducted in three European countries on the effect of lamp spectrum on face recognition and the perception of safety and comfort outdoors are presented. The results consistently show that at comparable illuminances, people perceive areas illuminated with white light to be brighter, safer and more comfortable than the same neighbourhood illuminated with yellowish light.

The effects of red and blue light on alertness and mood at night

Abstract: This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self-assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12—30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night.

A rules of thumb-based design sequence for diffuse daylight

Abstract: This paper proposes and validates a daylighting design sequence for sidelit spaces. Since the design sequence uses the daylight factor as a performance metric, it is aimed towards spaces that primarily receive diffuse daylight. It should be complemented by a design analysis that looks at direct sunlight for glare and energy considerations. The sequence interconnects and refines earlier proposed rules of thumb and is intended to be used during the earliest design stages when concepts regarding programming, floor plans, massing and window areas are initially explored. All steps within the sequence were ‘validated’ using Radiance simulations of over 2300 sidelit spaces. During step one of the sequence the effective sky angles are calculated and target daylight factors are defined for all potential daylit zones within a building. In step two a refined version of the ‘daylight feasibility study’ is used to help the design team to identify building zones with high daylighting potential based on a target mean daylight factor criterion. During step three suitable interior room dimensions and surface reflectances are determined using a combination of the Lynes’ limiting depth, ‘no sky line’, and window-head-height rules of thumb. Step four provides a more accurate estimate of the required glazing area for each zone based on the Lynes daylight factor formula which is also validated as part of this work. The effect of external obstructions is considered throughout the process. The paper closes with a discussion of the merits of the design sequence compared to the glazing factor spreadsheet calculation method promoted by LEED-NC 2.2.

Stimulus range bias explains the outcome of preferred-illuminance adjustments

Abstract: Review of previous studies suggests that mean preferred illuminances determined using an adjustment task tend to lie in the middle of the range of illuminances available, a stimulus range bias. This hypothesis was validated through the results of an experimental study. It is therefore suggested that the adjustment task is not an appropriate method for determining optimum illuminances.

A Method for Assessing the Visibility Benefits of Roadway Lighting

Abstract: Photometrically accurate lighting software and a model of visual performance were used to evaluate realistic roadway lighting and driver scenarios A great deal of data, both virtual photometric quantities and values of relative visual performance, were generated A method for simplifying these data was developed to create practical insights about the value of different fixed roadway lighting systems In particular, it was concluded that it is important to illuminate both high- and low-speed intersections, to provide high illumination for older drivers on high-speed roadways with intersections, and perhaps to incorporate refined photosensor-based control of lighting in highly developed areas The approach used here enables officials responsible for public cost and public safety to make more sophisticated and rational decisions about roadway lighting

Towards hybrid lighting systems: A review:

Abstract: This paper reviews developments in hybrid light guidance systems. In these daylight and electric light are simultaneously delivered into a building where they are combined and distributed via lumin...

Ecological measurements of light exposure, activity, and circadian disruption.

Abstract: In humans, circadian rhythms have an average period of 24.2 hours. The 24-hour patterns of light and dark on the retina synchronise circadian rhythms to the local time on earth. Lack of synchronisation between the endogenous clock and the local time has been associated with a host of maladies. Therefore, it is important to measure circadian light exposures over the course of the 24-hour day and to be able to assess circadian entrainment and disruption in actual living environments. Presented is an overview of the recently developed Daysimeter, a personal measurement device for recording activity and circadian light exposure. When the Daysimeter is worn on the head, two light sensors near the eye are used to estimate circadian light exposures over extended periods of time. Phasor analysis combines the measured periodic activity-rest patterns with the measured periodic light—dark patterns to assess behavioural circadian entrainment/disruption. As shown, day-shift and rotating-shift nurses exhibit remarkably different levels of behavioural circadian entrainment/disruption. These new ecological measurement and analysis techniques may provide important insights into the relationship between circadian disruption and well-being.

Light and corporate identity: Using lighting for corporate communication

Abstract: The central focus of this study is to investigate what potential exists for brand communication in the lighting of retail outlets. Lighting not only facilitates the visual task, helping to present the merchandise and contributing to the feeling of well-being, but can also augment the communication of a brand’s appearance. For this study, computer visualisations of retail outlets with different lighting variations are evaluated in terms of light, spatial setting and brand impression by regional and international groups using the semantic differential technique. A comparison between rooms with and without luminaires yet with the same lighting effect demonstrates the effect of luminaires as design objects. From the results it can be deduced that light can be used for brand communication in order to define the image of a company more clearly.

Impact of current supply on LED colour

Abstract: The quality of light emitted by lighting systems based on high brightness LEDs is studied using colorimetric parameters (chromaticity coordinates, correlated colour temperature and colour rendering index) when operating with different forms of electrical power supply (continuous and pulsed current). Uncertainties, calculated by Monte Carlo simulations applied to relative spectral measurements and colorimetric parameters are presented.

A pilot study of lighting and low vision in older people

Abstract: We investigated the influence of lighting on performance at activities of daily living in 24 older people with low vision from cataract and/or macular degeneration. Participants carried out four everyday tasks, each at three illuminances: 50 lux, 200 lux, and 800 lux. Both objective performance and subjective preference were recorded. Subjects tend to perform better under brighter conditions, but the average results masked large individual variations. Indeed, most participants showed a large effect of lighting on performance in at least one task, but the optimal light level varied idiosyncratically from one subject to another. The best approach to provide optimal lighting for older people with low vision may be to individually assess their preference and performance at different light levels.

Validating the application of occupancy sensor networks for lighting control

Abstract: A new occupancy detection sensor network was developed, commissioned and installed in two private offices: data were collected to evaluate the utility of the sensor network for lighting control. Re...

A comparison of simultaneous and sequential brightness judgements

Abstract: This paper presents the results of brightness matching and brightness discrimination tests carried out using sequential evaluation (temporal juxtaposition) to compare brightness under lamps of different spectral power distribution at mesopic levels of illumination. These data are compared with the results of previous tests, which used simultaneous evaluations (spatial juxtaposition) to enable comparison of these different modes of evaluation. It is concluded that sequential and simultaneous evaluations yield similar estimates of illuminances required for equal spatial brightness and similar levels of precision in this task.

Optimisation and design of ducted daylight systems

Abstract: There is growing interest in the use of ducted daylight systems as a means of increasing the natural lighting of buildings Such systems are also known as ‘daylight guidance’, ‘tubular rooflight’ o

Influence of ambient lighting in a vehicle interior on the driver’s perceptions

Abstract: An experimental study on the effects of vehicle ambient lighting on the subjective perception of the driver has been conducted. In an experimental vehicle 12 different ambient interior lighting scenarios were displayed to 31 people while driving in an immersive simulation which created a visual environment similar to a night drive. After each experimental run the driver answered different questions on their perception of the vehicle interior under the different lighting scenarios. The results showed that ambient lighting, although being in a peripheral position in the driver’s field of view, has several significant positive influences on space perception, interior attractiveness, perceived safety, functionality and perceived interior quality.

Daylight in atrium buildings: Geometric shape and vertical sky components

Abstract: This study investigated the impact of well geometry on vertical sky components in atria with square and rectangular forms under a CIE standard overcast sky. By comparing scale model measurements and analytical theory the vertical sky components, calculated using Radiance, were validated. More simulated data of vertical sky components for a very wide range of atrium geometries are given. From the results the attenuation of the vertical sky component on the wall of a square atrium is explained and some empirical functions are derived. In addition, the results from atrium models with rectangular floor plans show the relationships between the vertical sky component and the plan aspect ratio. Some guidelines for design are presented.

Overcast sky luminance is dependent on the physical state of the atmosphere below cloud level

Abstract: An approximate formula for sky luminance under overcast conditions taking into account different pollution content of the atmosphere is determined. The homogeneous cloud layer is considered to be a constant source of light, while the undercloud atmosphere is taken as a single scattering medium. The final mathematical expressions depend on turbidity and scattering ability of the undercloud atmosphere as well as on the altitude of the clouds. Such a parameterised model is therefore easily scalable and well adjusted to the actual meteorological situation (contrary to empirical models in current use). The derived analytical formula is suitable for engineering practice to perform rapid simulations of sky luminance.

Comparison of conventional and accelerated lifetime testing of fluorescent lamps

Abstract: Based on experimental data published by others, this paper examines the veracity of an expression relating the lifetime of fluorescent lamps, with ballasts to factors that contribute to electrode degradation, using different on and off times in the durability tests. Further, the relationship between conventional and accelerated durability tests characterised by different fluorescent lamp continuous operation and off times are analysed, revealing that the accelerated tests are not always shorter. Finally, based on experimental measurements of the parameters that determine lamp lifetime, the effect of applying accelerated testing to a set of lamps that had previously been subjected to a conventional durability test is analysed.

Using satellite-based methods to predict daylight illuminance for subtropical Hong Kong

Abstract: Satellite-based methods are proposed to estimate global illuminance from geostationary satellite data under local climate conditions. The data used in this model are global irradiance and global illuminance collected from the International Daylight Monitoring Programme research class station in The Chinese University of Hong Kong and the visible channel data of the Geostationary Operational Environmental Satellite 9 from May 2003 to May 2005. The proposed methods consist of an indirect method, which derives global irradiance from satellite images first and then converts global irradiance to global illuminance by a luminous efficacy model, and a direct method, which derives global illuminance directly from satellite images. The root mean squared errors of hourly global illuminance are 35% and 32% for the indirect and the direct methods, respectively.

The 250th anniversary of daylight science: Looking back and looking forward

Abstract: This year it is appropriate to celebrate an event of great significance for all illuminating engineers. This year is the 250th anniversary of the publication of major books by Pierre Bouguer and Jo...

Book review: Boyce P and Raynham P (2009) The SLL Lighting Handbook, The Society of Light & Lighting, London. 303 pp. Soft cover. £80 (£40 for CIBSE members). ISBN 978-1-906846-02-2:

Abstract: This brilliantly put together book, published to coincide with the SLL Centenary celebration is a first and much needed comprehensive lighting handbook from the Society of Lighting and Lighting. This book is full of valuable data and practical information on light and lighting and is an essential tool to be placed handy on every lighter’s book shelf. The soft cover, handy sized (A5) book is printed on quality paper giving it a good feel and the text is easy to read and well supported by pictures and diagrams. The rich and valuable information is aimed at lighting practitioners and students of lighting. The authors have done a great job in squeezing in so much interesting and helpful information into this compact book. The book is well laid out with the content sorted into three broad parts and further subdivided into 23 chapters. For rapid search of subjects the page edges of each chapter are coloured to the same colour code as used for the content list titles. Although the book heavily concentrates on lighting techniques and applications never the less it deals well with the basics of light, vision and equipment characteristics. Part 1 of the book deals with Fundamentals split into two chapters, Light its nature and measures, and Vision, its characteristics and perception. Here of particular interest is figure 2.15 which shows the impact lighting conditions make on visual performance and forms the basis for the task illuminance recommendations. The treatment of visual discomfort is superb and a must to read by all who design lighting schemes by software. However, there are many novel terms used in this and other parts of the book and a section defining these terms or on the language of light would have been very beneficial to some users of this book. It is a pity that no reference is made to BSEN 12665 the standard on practical light and lighting definitions. Part 2 covers Technology in three chapters, Light sources, Luminaires and Electrics. The light sources chapter gives insight to the production of light including daylight and follows up with the details of the construction, operation and characteristics of all currently used electric lamps including LEDs. The chapter gives much information on the GLS filament lamp and some poor efficacy discharge lamps although these are in process of being phased out from the supply chain by the implementation measures of the EuP Directive (an EU law). The Luminaires chapter describes the basic requirements of materials, optics, construction features and operational characteristics of many types of luminaires used for indoor and outdoor lighting. There are liberal examples illustrated for re-inforcement. The chapter ventures beyond photometric performance to discuss also airhandling and acoustic behaviour of some indoor luminaires. The electrics chapter concentrates on control gear circuits and lighting control techniques. The reader will learn how ballasts, transformers, LED drivers and dimmers operate but not much on their construction or performance characteristics. Part 3 Applications covering indoor and outdoor lighting application segments forms the bulk of the book. It is heartening to find that the guidance and advice is not restricted to the popular office, education, hospital, road and sports lighting segments but bravely the Lighting Res. Technol. 2010; 42: 123–124

Prediction of fluorescent lamp lifetimes with accelerated testing

Abstract: This paper proposes a method for predicting fluorescent lamp lifetimes based on a minimum number of accelerated life tests. This prediction allows the life of the lamp in continuous operation to be...

Mesopic spectral sensitivity curves by a colour-matching method

Abstract: A new model for mesopic spectral sensitivity curves is realised, using the colorimetric method. Trichromatic colour matches to five monochromatic stimuli are made within the mesopic range of vision at various levels of power using monochromatic primaries. The proposed model is a linear combination of the V10(λ) and V'(λ) standard spectral sensitivity curves and is characterised by a coefficient depending on radiance. The values of this coefficient are first estimated from the colorimetric results using the least squares method. Then, they are fine tuned by an optimisation procedure. This model gives comparable results to other models based on visual performance.

A relation between mass loss and life of incandescent filament lamps

Abstract: The thermodynamics of a radiating and evaporating tungsten filament having a hot-spot defect are examined theoretically. Assuming quasi-steady-states for the main and the hot-spot segments, the time profiles of their temperatures and radii are derived in closed form. Explicit relations among the fractional mass loss, failure time and defect size ratio are obtained and compared against approximate expressions used by Gluck and King7 and by Elenbaas.14 Numerical results computed for vacuum lamps support our theory.

Editorial: Lighting under pressure

Abstract: There can be little doubt that lighting is under pressure. Most of this pressure is coming from those who are concerned about global warming/sustainability. What these people want to see is a reduction in the use of electricity, particularly electricity generated through the burning of fossil fuels. Their impact is evident in the de facto banning of the incandescent lamp in many countries. But why lighting? Are there no other users of electricity to be considered? There undoubtedly are but what makes lighting an attractive target for electricity savings are four characteristics. Lighting installations constitute a major user of electricity; they have a much shorter life than buildings; they are easy to modify in existing buildings and they are conspicuous so changes in lighting makes it obvious that the authorities are doing something. Faced with this onslaught, the initial response of the lighting community is usually to emphasize the importance of maintaining lighting quality. This is followed by suggestions about how to lower electricity consumption. There are usually three possibilities suggested; a greater use of daylight combined with better controls on electric lighting, the development of more energy efficient lighting technology and a higher proportion of carbon-free electricity generation in the fuel mix. Unfortunately, these three possibilities will not do. They are, respectively, too slow, too uncertain and too expensive. The only honest answer to a demand for rapid and major reductions in the electricity consumed by lighting is a reduction in the illuminances used in new and existing installations. Would this be a disaster? The first thing to say in answer to this question is that illuminance recommendations are not written in stone. There have always been differences in illuminance recommendations between countries and, even for the same country, the recommendations have varied over the decades. The second is that as regards visual performance, illuminance is a second order effect relative to visual size and contrast. This means that if you are concerned that reducing illuminance will lead to deterioration in visual performance, you can always offset it by increasing either the size or contrast of the target details. The third is that for self-luminous computer displays, decreasing illuminance will improve visibility. A more serious difficulty is that people like what they are used to and may consider any reduction in illuminance to be a backward step. This objection might be overcome by ensuring the brightness of the space is maintained either by choosing an appropriate light spectrum or light distribution. In any case, it is important to appreciate that the reduction in illuminance need not be very large to have a significant effect on electricity use. The fact is the response of the human visual system to illuminance is broadly logarithmic while the influence of changing illuminance on electricity demand is broadly linear. As the Chinese say ‘‘May you live in interesting times’’ We do, and they look like becoming even more interesting. The lighting community needs to consider how it is going to respond to the pressure upon it; to fight for current standards, to accept defeat and take whatever the politicians impose or to use our knowledge to maximize the benefits of lighting while minimizing the environmental costs. You choose.