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Illumination Level (illumination + level)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

An expert system for lighting energy management in public school facilities

EXPERT SYSTEMS, Issue 4 2006
Daniel J. Fonseca
Abstract: Lighting accounts for a large part of the energy expenses of a facility, ranging from 40% to 60% of the total energy cost. Therefore, it represents a critical factor to consider in any energy management program. Lighting audits involve complex energy calculations, such as the estimation of light intensity per square unit area, quality of illumination, and required number of light sources to obtain an adequate illumination level in the facility. In this paper we discuss the development and implementation of an easy-to-use expert system for lighting energy management in public schools. The prototype computer-based system can evaluate 11 different areas of a school facility, and it can identify suitable lighting solutions from 17 distinct bulb types and 38 ballast types. The system determines a facility's required number of bulbs, and it performs the cost and saving analysis of its final recommendation. The constructed expert system was successfully validated by two human experts through two case studies, involving the evaluation of a conventional classroom and a medium-size office. [source]

Into the twilight zone: the complexities of mesopic vision and luminous efficiency

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2006
Andrew Stockman
Abstract Of all the functions that define visual performance, the mesopic luminous efficiency function is probably the most complex and hardest to standardise or model. Complexities arise because of the substantial and often rapid visual changes that accompany the transition from scotopic to photopic vision. These are caused not only by the switch from rod to cone photoreceptors, but also by switches between different post-receptoral pathways through which the rod and cone signals are transmitted. In this review, we list several of the complexities of mesopic vision, such as rod,cone interactions, rod saturation, mixed photoreceptor spectral sensitivities, different rod and cone retinal distributions, and the changes in the spatial properties of the visual system as it changes from rod- to cone-mediated. Our main focus, however, is the enormous and often neglected temporal changes that occur in the mesopic range and their effect on luminous efficiency. Even before the transition from rod to cone vision is complete, a transition occurs within the rod system itself from a sluggish, sensitive post-receptoral pathway to a faster, less sensitive pathway. As a consequence of these complexities, any measure of mesopic performance will depend not only on the illumination level, but also on the spectral content of the stimuli used to probe performance, their retinal location, their spatial frequency content, and their temporal frequency content. All these should be considered when attempting to derive (or to apply) a luminous efficiency function for mesopic vision. [source]

Age-related lens yellowing per se contributes little to the increase in Farnsworth-Munsell 100 hue error scores with age

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008
Raymond O. Beirne
Purpose:, To investigate the effects of real and simulated age-related changes in crystalline lens yellowing on Farnsworth,Munsell (FM) 100 hue total and partial error scores. Methods:, FM 100 hue total and partial error scores were measured in a group of younger (n = 10, mean age 22.2 ± 2.65 years) and a group of older (n = 10, mean age = 54.5 ± 2.64 years) normal observers along with psychophysical estimates of crystalline lens optical density and pupil size measurements. Three younger observers underwent repeated FM 100 hue testing using a variety of simulated age-related lens yellowing conditions, using filters with well-defined absorption properties which mimicked the real age-related lens yellowing changes of the older group. FM 100 hue scores were also measured under different levels of background illumination and pupil size in the 3 younger observers. Results:, FM 100 hue total and partial error scores were significantly higher in the older age group compared to the younger group (p <0.01). Lens density measures were significantly higher in the older age group compared to the young group (p<0.01), but showed less scatter with age than FM 100 hue error scores. Pupil size was significantly larger in the younger group compared to the older group (p<0.01). Simulated lens yellowing in the three younger observers, equivalent to the level of that of the older observers, did not affect any of their FM 100 hue total or partial error scores. Reductions in pupil size and illumination significantly affected the younger observers' performance, with increases in error score equivalent to the observed age-related decline between the younger and older group. Conclusions:, Lens yellowing per se makes little contribution to the increase in Farnsworth,Munsell 100 hue error score with increasing age. Retinal illumination levels and pupil size can significantly affect the error score and should be considered when interpreting FM 100 hue error scores in older subjects. Clinicians should also consider iris colour and macular pigment density when interpreting FM 100 hue error scores. [source]

GaAs converters for high power densities of laser illumination

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2008
E. Oliva
Abstract Photovoltaic power converters can be used to generate electricity directly from laser light. In this paper we report the development of GaAs PV power converters with improved conversion efficiency at high power densities. The incorporation of a lateral conduction layer (LCL) on top of the window layer resulted in a considerable gain in efficiency at high illumination levels. Additional performance improvements were obtained by using a metal electrode grid design and antireflection coating optimised for monochromatic and inhomogeneous laser light. Maximum monochromatic (810,nm) optical-to-electrical conversion efficiency of 54·9% at 36·5,W/cm2 has been achieved. The characteristics of laser power converters with p/n and n/p polarity are discussed in this paper. Moreover, different materials and doping levels were applied in the LCL. The performance of these different device structures at high laser intensity is presented and discussed. It is shown that the lateral series resistance of the cell has a major impact on the overall device performance. Copyright © 2008 John Wiley & Sons, Ltd. [source]