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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 1     july 2006

Publisher's data


Editorial:

THE INTERTWINED FUTURE OF COMPUTING AND LIGHTING DESIGN

Articles:

DYNAMIC DAYLIGHT PERFORMANCE METRICS FOR SUSTAINABLE BUILDING DESIGN

C.F. REINHART, J. MARDALJEVIC, AND Z. ROGERS

The use of dynamic daylight performance measures for sustainable building design is promoted. The shortcomings of conventional, static daylight performance metrics which concentrate on individual sky conditions, such as the common daylight factor, are explored. A review is provided of previously suggested dynamic daylight performance metrics, and the capability of these metrics to lead to superior daylighting designs and their accessibility to non-simulation experts is discussed. Several example offices are examined to demonstrate the benefit of basing design decisions on dynamic performance metrics as opposed to the daylight factor.

LIGHT FLICKER-FACTOR AS A DIAGNOSTIC QUANTITY FOR THE EVALUATION OF DISCHARGE INSTABILITIES IN HID LAMPS

FARHANG AFSHAR

There are some phenomena in High Intensity Discharge (HID) lamps which have the potential to make the discharge unstable. Discharge instability, can lead to some transients in light intensity, or in its periodic form, to annoying light flickering. Instabilities appear in a very vast range. Depending on the strength of the source of instability, it varies from a very slight deflection of sodium sheath to extreme deviations of conducting channel from its normal position which can extinguish the lamp as well. In order to detect the existence of such phenomena and predict their potential power, their effects and consequences on the light intensity can be analyzed. This has been done by using a tuned model of the human eye-brain system, to predict the perceptibility of the transient changes of light. The purpose of this paper is to introduce the ’light flicker factor’ based on eye-brain model as a measure of discharge instabilities. The implementing method of the model and a proper measuring system for light flicker factor is being discussed. Some laboratory experiments to support this method of measurement are presented.

CALCULATION OF OCCLUDED DIFFUSE AND NONDIFFUSE RADIATIVE EXCHANGE FORM FACTORS

D.L. DILAURA

A procedure is described to calculate the radiative exchange form factor between polygons. The spatial distribution of the emitting surface can be arbitrary and occluding surfaces are taken into account. Emitted radiant power is discretized into collimated, homogeneous beams leaving in a 3-dimensional, angular spray. Since a beam is homogeneous, the flux transported to a receiving surface is proportional to the intersection area of beam and surface. Occluding surfaces change the shape of the areas of intersection by casting collimated shadows. The total radiant power transported is proportional to the sum of the areas of intersection of all beams. Test cases are presented that demonstrate the utility and accuracy of the procedure and compare the computational expense with ray casting.

HIGHER COLOR TEMPERATURE LAMPS MAY NOT APPEAR BRIGHTER

X. HU, K.W. HOUSER, D.K. TILLER

This study examines the belief that rooms illuminated with higher correlated color temperature (CCT) lamps will appear brighter than rooms illuminated with lower CCT lamps at the same illuminance. This belief is held by many illuminating engineers and lighting designers, despite the fact that it is not supported by theory, and has received mixed support in experimental studies. The linear brightness models of Guth and Howett, and the nonlinear color appearance models of Nayatani and Hunt predict that higher CCT sources will appear dimmer than lower CCT sources, though the predicted brightness differences are small. We report results from two experiments to test the predictions of these models. Both experiments involved the visual comparison of two identical side-by-side full-scale rooms. One room was illuminated with lamps having a nominal CCT of 3500K; the other room was illuminated with lamps having a nominal CCT of 6500K. All other photometric characteristics of the two rooms were held constant and the rooms were identically furnished as mirror images with typical office furniture. In the first experiment forty-one subjects used a forced choice survey instrument to identify which room appeared brighter. In the second experiment twenty-eight subjects used a dimming adjustment task to match the brightness in the two rooms. No relationship was found between CCT and perceived room brightness in either experiment. Evidence from linear brightness models, non-linear color appearance models, and the results of the psychophysical experiments reported here suggests that that there is no relationship between CCT and the perception of interior brightness. Although brightness perception is related to the spectral power distribution of an illuminant, CCT is too limited to characterize the relationship between source color and perceived brightness.

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