Lighting Research and Technology recent issues

Editorial

van Bommel, W. — Wed, 02 Sep 2009 06:25:37 PDT

Energy efficiency in lighting -- considerations and possibilities

Loe, D. — Wed, 02 Sep 2009 06:25:37 PDT

Energy efficiency is a prime consideration for all lighting professionals with reasons ranging from the threat of climate change through burning fossil fuels to the sustainability and availability of energy supplies as well as rapidly increasing costs. But it must be balanced against the need for well-lit environments to ensure the productivity, well-being, safety and health of the people it serves. A well-lit environment must provide both visual function and visual amenity for the particular application and for the architecture, together with an efficient use of energy. This means considering all the elements that contribute to the design and operation in an all-embracing manner. The challenge now is to address more critically the design, operation and specification of electric lighting in combination with available daylight. This will require new thinking and research to achieve satisfactory, efficient environments that will need investment for optimum results. But the outcome could be a long-term benefit to society with the benefit being greater than the sum of the parts.

Lamps for improving the energy efficiency of domestic lighting

Jacob, B — Wed, 02 Sep 2009 06:25:37 PDT

Change is coming to the domestic lighting market. The light source that has dominated domestic lighting since the birth of electric lighting is going to be squeezed out and others with different characteristics will replace it. Some of these are already on the market, some are entering the market now and some have yet to make an entrance. The householder is certainly going to have plenty of lamp types to choose from, all of them claiming to be ‘low energy’. Alternative domestic light sources include compact fluorescents which produce enormous energy savings over the incandescent lamp, but do not have its visual appearance, colour quality or instantaneous full light output. Tungsten halogen lamps do possess the light qualities of the incandescent lamp and are available in the traditional light bulb shape, but do not provide the same energy savings as compact fluorescents. LED’s are potentially the ideal replacement for incandescent lamps having a long life with a discrete appearance, but improvements to efficacy for the warm white version are required to meet Building Regulations. Research on OLEDs continues, but current usage is limited to display applications, a situation which may not change for some years.

Measurement and specification of lighting: A look at the future

Goodman, T. — Wed, 02 Sep 2009 06:25:37 PDT

Measurement is at the heart of our modern technological world, supporting trade, industry and science and underpinning the regulatory framework that helps maintain and improve our quality of life in areas as diverse as public health and safety, climate change, and sport and leisure. Unlike a large proportion of the millions of measurements made each day, those relating to things we can ‘see’, such as lamps and lighting, are not based only on physical parameters, but must also take account of the human visual responses. This paper explores the shortcomings in our current measurement systems for light and lighting, and highlights where further research is needed in order to understand more fully the ways in which light affects us. The latest advances in instrumentation and data analysis techniques are also reviewed and the potential consequences for measurements of lighting and glazing are considered.

Road lighting and energy saving

Boyce, P., Fotios, S, Richards, M — Wed, 02 Sep 2009 06:25:37 PDT

This paper examines how the lighting of roads in the UK might be changed so as to preserve the benefits while minimising energy consumption. It is divided into four sections, these being changes in technology, changes in patterns of use, changes in standards and contracts and changes in the basis of design. Useful changes in technology and patterns of use are available now, but their use will raise the question as to whether or not environmental considerations can override conventional financial constraints. Changes in standards and the basis of design are much more long term. Comparisons of road lighting standards used in different countries show significant differences that deserve examination. As for the basis of design, consideration of the importance of light to fatal and personal injury accidents of different types suggests that road lighting should be concentrated where pedestrians are common, not where speeds are highest. Ultimately, considering carefully what problem road lighting is intended to solve and whether or not road lighting is the best answer is the key to minimising the energy consumption of road lighting without diminishing road safety.

Daylight metrics and energy savings

Mardaljevic, J, Heschong, L, Lee, E — Wed, 02 Sep 2009 06:25:37 PDT

The drive towards sustainable, low-energy buildings has increased the need for simple, yet accurate methods to evaluate whether a ‘daylit’ building meets minimum standards for energy and human comfort performance. Current metrics do not account for the temporal and spatial aspects of daylight, nor of occupants comfort or interventions. This paper reviews the historical basis of current compliance methods for achieving daylit buildings, proposes a technical basis for development of better metrics, and provides two case study examples to stimulate dialogue on how metrics can be applied in a practical, real-world context.

Good lighting with less energy: Where next?

Richards, M, Carter, D — Wed, 02 Sep 2009 06:25:37 PDT

Book review: Cuttle C (2008) Lighting by Design. 2nd Edition, Oxford: Architectural Press. 243 pp. Colour and black and white illustrations. Soft covers. {pound}34.99 ISBN 978-0-7506-8768-3

Bean, R. — Wed, 02 Sep 2009 06:25:37 PDT

Editorial

Mardaljevic, J. — Wed, 27 May 2009 08:03:03 PDT

A model for the explanation of discomfort and pain in the eye caused by light

Stone, P. — Wed, 27 May 2009 08:03:03 PDT

A theoretical model is proposed for the explanation of discomfort and pain in the eye induced by light, based on known facts about the functioning of the nervous system and on experimental work reported in the literature. It is suggested that the iris, lens, facial muscles and extraocular muscles act as a linked servo-system in responding to lighting conditions. When the latter are excessive relative to retinal processing ability, strain is imposed on the system and this initiates activity in the trigeminal nucleus. Use is made of the gate control theory of pain in suggesting a modulation process at the trigeminal nucleus on the incoming discomfort or pain message which ultimately receives interpretation and control at a higher level of the brain. The model embraces discomfort glare and photophobia within the same framework and provides potential explanations for the wide ranging conditions in which photophobia and sensitivity to light are observed.

An experimental study of a facade mounted light pipe

Duc Hien, V., Chirarattananon, S. — Wed, 27 May 2009 08:03:03 PDT

An experimental study of a rectangular light pipe mounted on a façade is reported. We used static and adjustable reflectors for enhancing capture and transmission of sunlight through the light pipe. A ray tracing technique was used to calculate the direct sunlight reflected into the light pipe and its transmission to the end of the light pipe. An inter-reflection method was used to calculate the transmission of diffuse skylight and the resulting daylight illuminance in the building interior. The experimental and calculation results demonstrate that daylighting through light pipes can provide acceptable illuminances in deep spaces for almost the whole day under conditions of clear and partly cloudy skies.

A camera as a sensor for lighting and shading control

Newsham, G., Arsenault, C. — Wed, 27 May 2009 08:03:03 PDT

We developed a proof-of-concept prototype camera-based system for lighting and shading control. The system utilised a simple CMOS-based digital camera with an approximate v-lambda filter, calibrated to provide pixel luminance values up to 10,000 cd/m². We demonstrated that the single camera sensor has the potential to replace the multiple sensors required by conventional systems for daylight harvesting, shading control and occupancy sensing. Performance similar to conventional systems was replicated, but in addition, alternate control algorithms based on spatial luminance information were demonstrated. However, considerable further development would be required to produce a commercial version, and there may be resistance to deployment due to privacy issues. Cameras offer other potential valuable end uses, examples are fire detection and security, which could effectively subsidise the lighting control functions, making automatic lighting controls more financially attractive, and promoting energy savings.

A colour harmony rendering index based on predictions of colour harmony impression

Szabo, F., Bodrogi, P., Schanda, J. — Wed, 27 May 2009 08:03:03 PDT

This study describes the development of a new measure intended to improve the description of light source colour quality. Previously, the authors have developed several colour harmony formulae to describe observers' impressions of colour harmony for two- and three-colour combinations seen under well-defined viewing conditions. One of the applications of these formulae is to quantify the distortion of colour harmony that can occur on changing from one light source to another. Based on the colour harmony predictions of these formulae for a sample set of colours seen under reference and test light sources a new light source colour quality metric, the `colour harmony rendering index', is defined. Two experiments were carried out to investigate the correlation between visual observations and this new colour quality metric.

Lifetime prediction of fluorescent lamps used in photovoltaic systems

Rosillo, F., Chivelet, N. — Wed, 27 May 2009 08:03:03 PDT

This paper approaches lifetime prediction of fluorescent lamps in photovoltaic systems by means of an analytical model. This can assist in improving ballast design and extending the lifetime of fluorescent lamps. As a result of our work, the temporal integral of the glow current to starting and the lamp voltage during normal operation normalised to nominal voltage appear to be the two independent variables that describe the influence of startup and continuous operation on lamp lifetime with an acceptable degree of accuracy. The analytical expression found explains 92.4% of the variability in lifetime. Model agreement with original data and its range of application and limitations are also analysed.

Book review: Lighting Guide 2: Hospitals and Health Care Buildings, The Society of Light and Lighting -- (2008), 87 pp, ISBN 978-1-903287-99-6

Moore, D. — Wed, 27 May 2009 08:03:03 PDT

Editorial

Cannon-Brookes, S. — Tue, 10 Mar 2009 07:48:47 PDT

Using digital cameras as quasi-spectral radiometers to study complex fenestration systems

Gayeski, N., Stokes, E., Andersen, M. — Tue, 10 Mar 2009 07:48:47 PDT

This work discusses the use of digital cameras fitted with absorption filters as quasi-spectral radiometers. By filtering incident light into selected wavelength intervals, accurate estimates of radiances can be made for unknown spectra. This approach is being employed as part of a new video-projection goniophotometer to study the properties of angularly and spectrally selective complex fenestration systems. Complex fenestration systems are increasingly being used to distribute solar radiation purposefully in buildings. They can be utilized to optimize energy performance and enhance daylighting. Radiance estimates from calibrated digital cameras enable the assessment of quasi-spectral, bi-directional scattering distribution functions of total radiance transmitted or reflected by a fenestration system over desired wavelength intervals. A silicon and an indium gallium arsenide digital camera are used to enable measurements across a 380 to 1700 nm wavelength interval.

Transmission illuminance proxy HDR imaging: A new technique to quantify luminous flux

Mardaljevic, J., Painter, B., Andersen, M. — Tue, 10 Mar 2009 07:48:47 PDT

A technique to measure arbitrarily complex luminous fluxes across large areas is presented. The technique is founded on high-dynamic range (HDR) imaging technology and can be achieved using a standard consumer digital camera and everyday materials such as printer-grade white paper. The same approach can also be used to determine the direct and diffuse components of illuminance. The technique has been named transmission illuminance proxy - high dynamic range imaging or TIP-HDRI.

The unified system of photometry applied to remote airfield lighting

Rea, M., Yuan, Z., Bierman, A. — Tue, 10 Mar 2009 07:48:47 PDT

A consortium of American universities was sponsored by the Federal Aviation Administration to develop technical specifications for remote airfield lighting systems that would be used for nighttime operations by general (non-commercial) aircraft. The results from three psychophysical experiments are presented here dealing specifically with the effects of light source intensity, colour and flash frequency on both objective and subjective measures of behaviour under simulated flight conditions. Of special significance, this study showed for the first time that the unified system of photometry developed by Rea et al. (2004) to model the relative contributions of rods and cones for a given visual task could also be used to model the relative contributions of rods and cones for sequential visual tasks.

User attitudes toward tubular daylight guidance systems

Carter, D., Al Marwaee, M. — Tue, 10 Mar 2009 07:48:47 PDT

The study reports quantity and quality of daylight delivered by tubular daylight guidance systems in large open plan offices. The daylight contribution was of the order of 25% of total design workstation illuminance giving daylight penetration factors of between 0.5% and 1.3%. User views suggest that tubular daylight guidance systems were inferior to windows in delivery of both quantity and quality of daylight although satisfaction with some aspects improves with increased daylight penetration

Evaluation of LED illumination for dental instruments

Li, C., Strassl, M., Rauchenzauner, S., Wintner, E. — Tue, 10 Mar 2009 07:48:47 PDT

White LEDs offer many advantages for use in dental instruments compared to the halogen light sources presently used. However, such LEDs have a very different spectral power distribution than halogen light sources. Therefore, the colour rendering properties of such LEDs have to be evaluated. The CIE colour rendering index is not suitable for this purpose so, in this study, a white LED designed for dental instruments was evaluated using the CIE E_L*a*b*2000 method and colour samples representative of teeth. From this evaluation, it is concluded that white LEDs have an advantage compared to halogen light sources for tooth colour evaluation by dentists.

Book review: Designing Lighting for People with Dementia, by Pollock, Richard; McNair, David; MacGuire, Brian; Cunningham, Colin (2008). Stirling: The University of Stirling in association with the Institution of Lighting Engineers. 41pp. soft covers. ISBN 978 1 85769 232 7

Tregenza, P. — Tue, 10 Mar 2009 07:48:47 PDT

Editorial

Carter, D. — Thu, 27 Nov 2008 08:34:49 PST

Estimating spectral information of complex fenestration systems in a video-goniophotometer

Stokes, E. C, Gayeski, N., Andersen, M. — Thu, 27 Nov 2008 08:34:49 PST

The effective use of complex fenestration systems in buildings requires knowledge of their optical spectral and directional properties. While the directional properties are commonly assessed by the measurement of bidirectional transmission or reflection distribution functions, the addition of spectral information would significantly aid in the design and analysis of such systems. This paper describes the development of a spectral estimation method that reconstructs reflectance and transmittance spectra of unknown complex fenestration samples in the Heliodome, an innovative video-goniophotometer. The estimation method relies on the digital output of a tri-chromatic charge-coupled device camera in eight filterbands to reconstruct a sample's spectrum using the truncated generalised singular value decomposition. This method is validated by comparing estimated spectra with documented reflectance and transmittance spectra of reference samples. In most spectrally selective materials, the method achieved average improvements of 50% over the Heliodome's previous quasi-spectral assessment method.

Computer simulation study of a horizontal light pipe integrated with laser cut panels in a dense urban environment

Kwok, C., Chung, T. — Thu, 27 Nov 2008 08:34:49 PST

A computer simulation study on the daylighting performance of a horizontal light pipe system integrated with laser cut panels at the entrance and output apertures was performed for two identical test rooms with different degree of obstructions in a dense urban environment under the CIE clear sky condition. It is observed that by properly varying the separation-to-thickness ratio and the aperture tilt angle of the laser cut panel at the entrance aperture, the illumination beneath the pipe emitter can be enhanced. It is concluded that due to the obstructed environment, the horizontal light pipe should aim at capturing light from high altitude sky and sun. An optimal set of STR and ATA values for the LCP at the entrance aperture of 0.5 and 35° respectively is found to be effective for both high and low floors in buildings within a dense urban context.

Compatibility of road lighting with star visibility

Soardo, P., Iacomussi, P., Rossi, G., Fellin, L. — Thu, 27 Nov 2008 08:34:49 PST

The influence of city lighting on astronomical observations is analysed by using a single parameter for a whole town based on the upward light from the luminaires. This parameter separates the influence of the upward light on the maximum visible stellar magnitude and on energy saving from the unavoidable reflections from the illuminated surfaces, independently of the way light is scattered in the atmosphere. It is shown that extreme reduction of spill light leads to no appreciable benefit for astronomy and increases installation and energy costs.

Indoor illumination by solar light collectors

Sansoni, P., Francini, F., Fontani, D., Mercatelli, L., Jafrancesco, D. — Thu, 27 Nov 2008 08:34:49 PST

An innovative system for illumination of internal spaces was studied, constructed and tested. The system was dubbed `The Sunflowers' because the solar collectors were designed to track the sun's position during the day. Each Sunflower includes sunlight concentrators, optical fibres and mechanical and electronic systems for sun tracking. A Sunflower lighting system has been successfully installed in a prestigious museum to provide internal illumination of showcases. Solar illumination is obtained by concentrating the sunlight into optical fibres, which guide the light in the interior of the building and realise the lighting points.

Effects of dimming 150 W ceramic metal halide lamps on efficacy, reliability and lifetime

Guest, E., Girach, M., Mucklejohn, S., Rast, U. — Thu, 27 Nov 2008 08:34:49 PST

Dimming high-intensity discharge (HID) lamps is often proposed as part of energy management schemes for lighting installations. However, the impacts of dimming on HID lamp performance are not well characterised. The impacts of operating 150W ceramic metal halide discharge (CMH) lamps for prolonged periods (up to 11 000 h) at reduced powers have been quantified. CMH lamps of 150W operated at 100W and 76W showed no significant differences in lumen maintenance, survival and colour rendering index compared to similar lamps operated at the rated power for the same time. The experiments confirm that the concept of dimming CMH lamps can be employed in roadlighting schemes, such as NumeLiTe, without detrimental consequences on lamp performance.

A physical model of the atmospheric aerosol turbidity for estimating the illuminance of direct sunlight

Brown, A. — Thu, 27 Nov 2008 08:34:49 PST

The aerosol turbidity index is the key variable in simple parameterisation models of direct normal solar radiation on a plane perpendicular to the direction of the sun. Techniques that use fixed design standard values of the turbidity index do not adequately account for variations in aerosol attenuation. This study presents a simple physical model to estimate the Unsworth—Monteith illuminance turbidity index T_Ui, using aerosol mass concentration (PM₁₀) data that are routinely available from air pollution monitoring stations. T_Ui is parameterised in terms of the aerosol scale height and the ground level aerosol extinction coefficient. A measured set of hourly average `clear sun' direct normal illuminances, and PM₁₀ data for the urban location of Sheffield UK was used to validate the proposed model.

Simple reaction times to chromatic stimuli: Luminance and chromatic contrast

O'Donell, B., Colombo, E. — Thu, 27 Nov 2008 08:34:49 PST

This paper examines the effect of colour on reaction times for variations in both luminance and chromatic contrast. Results confirm the idea that reaction times are determined by a cone-opponent mechanism: Reaction times generated in response to S-cone isolating stimuli are the longest, whereas the shortest reaction times are generated by L—M-cone isolating stimuli. In addition, an asymmetry between ON and OFF opponent channels is observed for stimuli modulated on the blue—yellow axis. Reaction time (RT) is influenced by hue and chromatic contrast at isoluminant condition. In the isoluminant condition, RT decreases as luminance contrast increases. At luminance contrasts of approximately 20%, RT approaches an asymptotic value, thus becoming independent of colour for further luminance contrast increases. This asymptotic value is achieved for lower luminance contrasts as chromatic contrast increases.

A new retinal photoreceptor should affect lighting practice

Berman, S. M — Thu, 27 Nov 2008 08:34:49 PST