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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 3     Number 2     October 2006

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Editorial:

THREE YEARS ON: A REPORT TO THE READERSHIP

Articles:

THE VIRTUAL LIGHTING LABORATORY: PER-PIXEL LUMINANCE DATA ANALYSIS DYNAMIC

MEHLIKA N. INANICI AND MOJTABA NAVVAB

The Virtual Lighting Laboratory (VLL) is an image based lighting analysis tool and methodology, which operates with physically-based High Dynamic Range (HDR) digital images. Through appropriate modeling, rendering, and image technology, physically based renderings and HDR Photographs can be used to extract per-pixel lighting information. In VLL, per-pixel lighting data extracted from physically based renderings is processed through mathematical and statistical operations to perform lighting analysis with detail, flexibility, and rigor that may be infeasible or impossible with the traditional lighting analysis approaches. The analysis in the VLL focus on the investigations of the following criteria to achieve the intended visual effect, performance, and comfort: adequate quantity of light; suitable spatial distribution of light; sufficient directionality of light; absence of glare; and sufficient spectral content of light.

THE POTENTIAL FOR DEMAND-RESPONSIVE LIGHTING IN NON-DAYLIT OFFICES

GUY R. NEWSHAM AND SANDRA MANCINI

Participants in an office laboratory had personal dimming control over lighting, and were then exposed to a simulated demand response (or “load shed”) involving dimming lighting by 2% per minute. Participants were given no expectation that the dimming would occur, and the principal measure used was the point at which participants intervened to restore light levels after the demand-response dimming began. Results showed that 20% of participants intervened by the time that desktop illuminance declined ~35% from their initial preferred level, and 50% of participants intervened by the time that desktop illuminance declined ~50%. Therefore, during a power supply emergency, dimming lights can contribute relatively large electricity demand reductions before lighting declines to a level where a substantial fraction of people would be motivated to seek a change.

LEDS FOR GENERAL ILLUMINATION: THE STATE OF THE SCIENCE

J. BRENT PROTZMAN AND KEVIN W HOUSER

Light emitting diodes (LEDs) are emerging as a viable source for the general illumination of the built environment. Recent product development efforts have focused on four areas: increased light output, increased conversion efficiency, minimization of color shifts, and increased color rendering index (CRI) for white LED sources. Although little can be argued against the first three areas of development, using CRI as a spectral design criterion may be misguided. Other measures of color preference or color discrimination may be better suited to optimize LEDs for general illumination. In the future, due to the nature of the LED spectral distributions, virtually any source spectrum may be possible, which begs the question: should product development efforts aim to match reference sources that are not optimal in terms of color preference or discrimination? This paper summarizes current theories about LEDs and color. Color shift is discussed as it relates to temperature, age, input current, and dimming. The methods of making white light with LEDs are described and contrasted in terms of chromaticity coordinates, correlated color temperature (CCT), and CRI. The colorimetric potential of LEDs is discussed in consideration of numerous measures of colorimetric performance .

ALLOWED LEVEL OF THE POWER RIPPLE IN LOW FREQUENCY SQUAREWAVE BALLASTS OF METAL-HALIDE LAMPS

FARHANG AFSHAR

In order to avoid the acoustic instabilities in metal halide (MH) lamps a proper method is to supply the lamp with a low frequency square wave current. Due to the topology of electronic ballasts for such an application, there is a high frequency ripple in the current or voltage waveform. It is known that such ripples with sufficient energy at the proper frequency are able to excite acoustic resonance in MH lamps. The threshold value for high frequency ripples in order to excite an acoustic mode and destabilize the lamp is under debate. This threshold is lamp dependent and should be measured experimentally for each lamp type. This paper addresses an automated experimental method to determine the threshold value of the power ripple in a frequency range of 10-400 kHz. The implementation of the proposed method which is based on the light flicker factor has been explained in a preceding paper. The experimental results show that less than 1% of power ripple at the resonance frequency is sufficient to excite a detectable (perceptible to the human eye) acoustic instability.

EFFECTS OF DEDICATED STOP-LAMPS ON NIGHTTIME REAR-END COLLISIONS

JUHA LUOMA, MICHAEL SIVAK, AND MICHAEL J. FLANNAGAN

This study was designed to evaluate whether dedicated stop lamps, in comparison to stop lamps that are functionally combined with tail or turn signals, provide additional safety benefits at night. The analysis compared the frequencies of rear-end collisions in which the vehicles were struck to those collisions in which the same vehicles were the striking ones. The analysis used 1999-2003 Florida and North Carolina crash data. The vehicle sample consisted of 38 passenger car models for the years 1994-2003. Overall, the results include a statistically significant pattern that suggests a beneficial effect of dedicated stop lamps. However, the results are complex and further analyses should be done to better understand the possible effect of dedicated versus combined stop lamps.

WHITE LED BASED ILLUMINATION SYSTEMS FOR INDIAN VILLAGES

K. R. SHAILESH

The need of energy efficient illumination systems for rural Indian homes is described, with an emphasis on the role of white LEDs in providing energy efficient illumination systems for rural homes. About two billion people in remote areas of developing nations have no electric lighting, a commodity industrialized nations take for granted. Poor lighting in homes hinders children’s learning, affects family health, and limits opportunities for a better life. White light-emitting diode supplies enough light for a child to read by. This simple but revolutionary technology can be supplied to homes and can light an entire rural village with less energy than that used by a single, conventional, 100-watt incandescent lamp.

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