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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 9 | Number 2 | October 2012

Publisher's data


Editorial:

History is Today


Articles:

PHOTOMETRIC IMPRECISION CAN LIMIT BUG RATING UTILITY

IAN ASHDOWN

The IES BUG rating system is useful for classifying outdoor luminaires when considering light trespass, sky-glow, and glare in accordance with the joint IDA-IES Model Lighting Ordinance (MLO). There are, however, limits to what can be measured in the laboratory. IES TM-15-11 requires that a luminaire with an uplight rating of U0 emits zero lumens into the upper hemisphere, while a U1 uplight rating or a G0 glare rating for high viewing angles requires fewer than 10 lumens. Given that the luminaire is emitting thousands of lumens and that the laboratory room surfaces have a diffuse reflectance of at least two percent, it is physically impossible to measure zero lumens, and extremely difficult to measure fewer than 10 lumens. Consequently, a U0 glare rating can only be obtained by physical examination of the luminaire and post-processing of the measured photometric data. Similarly, a U1 uplight rating or a G0 glare rating for high viewing angles is likely the result of data manipulation. The MLO User’s Guide should therefore be revised to provide a procedure within the ordinance text whereby an exception is allowed if a visual inspection of the physical luminaire shows that the uplight is negligible.

SPATIAL BRIGHTNESS PERCEPTION OF TRICHROMATIC STIMULI

MICHAEL P. ROYER AND KEVIN W. HOUSER

An experiment was conducted to examine the effect of tuning optical radiation on brightness perception for younger (18-25 years of age) and older (50 years of age or older) observers. Participants made forced-choice evaluations of the brightness of a full factorial of stimulus pairs selected from two groups of four metameric stimuli. The large-field stimuli were created by systematically varying either the red or the blue primary of an RGB LED mixture. The results indicate that light stimuli of equal illuminance and chromaticity do not appear equally bright to either younger or older subjects. The rank-order of brightness is not predicted by current models of human vision or theories of brightness perception including scotopic to photopic or cirtopic to photopic ratio theory, prime color theory, correlated color temperature, V(?)-based photometry, color quality metrics, linear brightness models, or color appearance models. Age may affect brightness perception when short-wavelength primaries are used, especially those with a peak wavelength shorter than 450 nm. The results suggest the need for the further development of a metric (or metrics) to predict brightness perception and that age should be included as a variable in such models.

A COMPARISON OF LIGHTING ENERGY MODELING METHODS TO SIMULATE ANNUAL ENERGY USE AND PEAK DEMAND

DARCIE CHINNIS AND GREGOR P. HENZE

Two simulation methods were developed to model the lighting energy use for a real office building and the results of those simulations were compared to submetered lighting energy data from that building. Three deterministic schedules and six stochastic first-order Markov-models were used to assess annual lighting energy density and peak demand density at both the officelevel and the building-level. The stochastic simulations, which apply only to the private offices, resulted in much lower annual energy density and peak demand density predictions due to interactions of users with the lighting and shade controls, and widely different daily use profiles. For the whole-building simulations, comparing all three deterministic schedules resulted in an inverse relationship between peak demand density and annual energy density; the closest correlation with the submetered data was found through the most building-specific but least empirically-vetted schedule-based simulation.

LIGHT POLLUTION INDEX (LPI): AN INTEGRATED APPROACH TO STUDY LIGHT POLLUTION WITH STREET LIGHTING AND FACADE LIGHTING

RIAD SARAIJI AND M. SAJU OOMMEN

Rather than being complementary, street lighting and façade lighting are typically designed independently of each other. As a result, light from street lighting luminaires might spill onto building façades and influence characteristics of the façade lighting including required light levels and color. Conversely, façade lighting might reflect onto the street and contribute to the street illumination. This manuscript presents an integrated approach to analyzing the interaction between the street and façade lighting in consideration of light pollution control. A generic street model with various calculation grids was studied. It was found that a moderately lit façade contributes to a horizontal illuminance of 5 lux or more on the street and a vertical illuminance of 4 lux or more 1.5 m above the sidewalk. An overilluminated street may result when both street and façade lighting exist without reference to each other. The size of the light-pollution calculation grid and the use of a 3-D illuminance graph were studied. It was found that fluctuations in the calculated amount of light pollution could occur unless the size of the pollution calculation grid is large enough to capture all of the upward flux. A method of achieving the optimal size of the calculation grid is demonstrated. Shortcomings of using light pollution percentage as a light pollution index are highlighted and an alternative light pollution index is proposed.

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