A Study of Near-Field Indirect Lighting Calculations

Mistrick, Richard G.; English, Cheryl R.

doi:10.1080/00994480.1990.10747970

Cited by 9 publications

(3 citation statements)

References 2 publications

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“…Some types of luminaires do not lend themselves to accurate photometry by the above-mentioned photometers. The photometric measurements of luminaires such as wallwashers, cove-lights and task-lights using these types of photometers are limited, and the accuracy of measure ment is sacrificed, 8 because these photometers were not designed specifically for measurements of these types of luminaire applications. Recently, several other photo metric techniques have been introduced, such as NearField photometry, 9 " 11 Luminance Field photometry 12 and Luminance Scans method.…”

Section: John Zhangmentioning

confidence: 99%

Linear Moving-Detector Photometer: A New Design Concept

Zhang

2004

Journal of the Illuminating Engineering Society

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Section: John Zhangmentioning

confidence: 99%

Linear Moving-Detector Photometer: A New Design Concept

Zhang

2004

Journal of the Illuminating Engineering Society

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“…In addition, expensive filament and/or reflector intersection problems often lead to inefficient ray tracing. Near-zone source 12,10,11,9 characteristics are usually ignored, as such models have only recently begun to appear .…”

Section: Raytracingmentioning

confidence: 99%

General near‐zone light source model and its application to computer‐automated reflector design

Siegel

1996

Opt. Eng

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The goal of this work is to develop a general light source model that is physically accurate, intuitively descriptive, computationally convenient, and applicable to real sources. This paper solves two major problems in illumination optics: near-zone general extended light source characterization for accurate image rendering and raytracing, and computer-automated reflector design using the resulting near-zone model. The main approach is to combine measurements with Fourier analysis, using judiciously chosen coordinate systems and orthogonal fitting functions. This approach has several advantages over standard raytracing: it provides for natural data compression and interpolation, it bypasses the problem of computing the radiance distribution of a real source by using actual pinhole CCD camera measurements, and it eliminates the computationally intensive ray-filament intersection problem by transforming the source into an equivalent nonuniform spherical radiator. A method for treating the occlusion of rays by the extended filament, with only spherical intersection calculations, is also discussed. The application of the method is illustrated by the problem of designing a smooth specular reflector to cast a desired intensity distribution on a distant screen for a given source. The problem becomes a straighforward numerical optimization of the perturbations to a base reflector shape. An algorithm to provide a first guess for the perturbations based on the shape of the image perimeter is also described.

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“…23 In a previous paper, 3 the authors reported the dif ferences in calculated illuminance values using farfield and near-field photometry. Mistrick and English 4 have reported that there are measurable dif ferences between actual measured values and calculated values using far-field photometry. These in vestigations, while valuable, were limited in scope and did not address the accuracy of near-field photometry when compared with actual lighting measurements.…”

Section: Introductionmentioning

confidence: 98%

On Computation Using Far-Field and Near-Field Photometry

Ngai¹,

Zhang²,

Quan³

1993

Journal of the Illuminating Engineering Society

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IntroductionThe current practice in photometric testing, evalua tion, and application relies on far-field photometry, which assumes a homogeneous area source. Unfor tunately, far-field photometry does not accurately model luminaire performance in applications where the luminaire is close to the illuminated surface. There is a clear need for a calculation system that predicts the lighting environment more accurately.Toward this end, the concept and techniques of near-field photometry have recently been inves tigated and developed using two approaches. One ap proach divides the luminaire into many small pieces, to find out the photometric characteristics of each point on the luminaire surface. 1 The other method is to find equivalent photometric distribution for specific applications. 23 In a previous paper, 3 the authors reported the dif ferences in calculated illuminance values using farfield and near-field photometry. Mistrick and English 4 have reported that there are measurable dif ferences between actual measured values and calculated values using far-field photometry. These in vestigations, while valuable, were limited in scope and did not address the accuracy of near-field photometry when compared with actual lighting measurements.In this paper, we will examine calculated values based on both far-field and near-field photometry, and compare these to actual measurements. The nearfield photometric approach that we have used is the equivalent photometric distribution method. 3 In short, we have taken actual measurements of lighting values of various types of luminaires at a series of distances and computed the same values us ing both far-field and near-field photometry, compar ing the differences. Luminaire selectionIn order to represent a variety of fluorescent lighting systems, three luminaires were selected for testing: a linear indirect luminaire, A; a furniture mounted luminaire, B; and a parabolic downlight luminaire, C.Luminaire A represents the most common type of linear indirect lighting system in use today, with wide spread photometric characteristics. The luminaires are normally installed 0.3-0.91 m (1-3 ft) from the ceil ing, and are suspended in continuous lengths. Because the luminaires are close to the ceiling, they benefit most from near-field photometry. Figure 1 shows luminaire A with an open top and a pair of side prismatic lenses. The luminaire is ap proximately 0.20 m (8 inches) wide and 1.22 m (4 ft) long with two 25-mm (T8) fluorescent lamps and a specular reflector.Luminaire B is an indirect lighting system designed for integration with the furniture in an office environ ment. The mounting distances are typically 0.61 m (2 ft) to 1.52 m (5 ft) from the ceiling. Unlike the con tinuous, linear luminaire, the furniture-mounted luminaire is a discrete unit, mounted individually; therefore, the luminance ratio on the ceiling is sen sitive to the accuracy of the intensity values not only along the length of the luminaire but perpendicular; to it as well. Figure 2 shows the cross-section of ...

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A Study of Near-Field Indirect Lighting Calculations

Cited by 9 publications

References 2 publications

Linear Moving-Detector Photometer: A New Design Concept

Linear Moving-Detector Photometer: A New Design Concept

General near‐zone light source model and its application to computer‐automated reflector design

On Computation Using Far-Field and Near-Field Photometry

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