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LEUKOS - The journal of the Illuminating Engineering Society of North America
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The Journal of the Illuminating Engineering Society of North America    Volume 5     Number 1     july 2008

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Editorial:

SEALS OF APPROVAL, LUMINAIRE RATINGS, AND OTHER BAD IDEAS

Articles:

PRELIMINARY METHOD FOR PROSPECTIVE ANALYSIS OF THE CIRCADIAN EFFICACY OF (DAY)LIGHT WITH APPLICATIONS TO HEALTHCARE ARCHITECTURE

CHRISTOPHER S. PECHACEK, MARILYNE ANDERSEN, AND STEVEN W. LOCKLEY

Recent studies have attempted to link environmental cues, such as lighting, with human performance and health, and initial findings seem to indicate a positive correlation between the two. Light is the major environmental time cue that resets the human circadian pacemaker, an endogenous clock in the hypothalamus that controls the timing of many 24-hour rhythms in physiology and behavior Insufficient or inappropriate light exposure can disrupt normal circadian rhythms which may result in adverse consequences for human performance, health and safety. This article addresses the problem of prospective analysis of building architecture for circadian stimulus potential based on the state of the art in photobiology. Three variables were considered in this analysis: lighting intensity, timing, and spectrum. Intensity is a standard design tool frequently used in illuminating engineering. Timing and spectrum are not commonplace considerations, so the analysis that follows proposes tools to quantitatively these additional requirements. Outcomes of photobiology research were used in this paper to define threshold values for illumination in terms of spectrum, intensity, and timing of light at the human eye, and were translated into goals for simulation – and ultimately for building design. In particular, the climate-based Daylight Autonomy (DA) metric was chosen to simulate the probabilistic and temporal potential of daylight for human health needs.

THE THEORY OF ACOUSTIC RESONANCE AND ACOUSTIC INSTABILITY IN HID LAMPS

FARHANG AFSHAR

This article reviews the current state of knowledge of acoustic instabilities in HID lamps. The phenomenon of acoustic instability has been investigated during the last four decades. However the exact physical backgrounds of this effect are still unclear. Based on the theory of acoustic streaming, a new explanation of the possible physical reasons for the excitation of acoustic instabilities and the temporal response of the discharge is given. To support the discussed hypothesis a real case of acoustic instability is investigated. It is shown that this hypothesis is able to explain some behaviors of the lamp discharge when an acoustic resonance is excited.

GRAPHICAL REPRESENTATION OF CLIMATE-BASED DAYLIGHT PERFORMANCE TO SUPPORT ARCHITECTURAL DESIGN

SIÂN KLEINDIENST, MAGALI BODART, AND MARILYNE ANDERSEN

Many conventional daylighting design tools are limited in that each simulation represents only one time of year and time of day (or a single, theoretical overcast sky condition). Since daylight is so variable – due to the movement of the sun, changing seasons, and diverse weather conditions – one moment is hardly representative of the overall quality of the daylighting design, which is why climate-based, dynamic performance metrics like Daylight Autonomy (DA) and Useful Daylight Illuminance (UDI) are so needed. Going one step further, the annual variation in performance (condensed to a percentage by DA and UDI) is also valuable information, as is the ability to link this data to spatial visualizations and renderings. Trying to realize this combination of analytical needs using existing tools would become an overly time-consuming and tedious process. The challenge is to provide all information necessary to early design stage decision-making in a manageable form, while retaining the continuity of annual data. This paper introduces a climate data simplification method based on a splitting of the year into 56 periods, over which weather conditions are “averaged” and simulated using Perez’s ASRC-CIE sky model, while information on sun penetration is provided at a greater resolution. The graphical output of the produced data in the form of “Temporal Maps” will be shown to be visually, and even numerically, comparable to reference case maps created using short time step calculations and based on illuminance data generated by Daysim.

THRESHOLD VISIBILITY LEVELS REQUIRED FOR NIGHTTIME PEDESTRIAN DETECTION IN A MODIFIED ADRIAN/CIE VISIBILITY MODEL

KURT W. ISING

Adrian’s Visibility Model is a useful tool for assessing the visibility of an object at night. However, it was developed using test data under laboratory conditions. Thus, it is necessary to determine the visibility levels which are required for target detection under nighttime driving conditions. The author has previously presented a study in which experimental data from Olson et al were applied to the Adrian Visibility Model to determine visibility levels at target detection for alerted and unalerted drivers. However, a limitation in the model’s handling of glare (valid for 1.5° to 30°) limited the useable data. A modified Visibility Model is proposed which incorporates the CIE General Disability Glare Equation. This widens the available glare range to 0.1° to 100° and allows for a more robust analysis than had been presented previously. Age, headlight beam pattern, and target reflectivity were all found to have a significant effect on visibility level at target detection for alerted drivers. Target size and position did not significantly affect visibility level at target detection. Average threshold visibility levels between 0.1 and 18 were calculated for alerted drivers. For unalerted drivers, average threshold visibility levels between 14 and 89 were calculated.

 

 

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