On Near-Field Photometry

Ngai, Peter Y.

doi:10.1080/00994480.1987.10748693

Cited by 16 publications

(8 citation statements)

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“…Again, a nice correspondence can be observed between values obtained using a photometer (dark black line), simulations from near-field data (circles) and a theoretical fit using equation (11) and a FWHM of 108 (grey line). When the distance to the source is small (R=D Array ¼ 5), two separate luminous intensity peaks are observed.…”

Section: Apparent Luminous Intensity Off the Optical Axis Of A Two-lesupporting

confidence: 53%

“…Near-field goniometry has indeed been known to offer a valuable alternative to far-field goniophotometry. [10][11][12][13][14][15][16][17][18][19] In a nearfield luminance goniometer, an illuminance meter and a luminance camera revolve around the light source. The luminance camera captures luminance maps 20,21 and the illuminance meter provides the absolute reference luminous flux data.…”

Section: Introductionmentioning

confidence: 99%

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Near-field and far-field goniophotometry of narrow-beam LED arrays

Jacobs

Forment

Rombauts

et al. 2014

Lighting Research & Technology

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In lighting calculations and simulations, the emission of a light source is conventionally modeled using the far-field luminous intensity distribution. However, the advent of luminaires including large arrays of LEDs with focusing optics creating narrow beams has made the traditional limiting photometric distance to reach far-field conditions less easy to determine. Furthermore, even correct far-field data can lead to erroneous predictions when illuminances are determined on a task surface which is positioned within the near-field region. A near-field representation could overcome these problems, but experimental validation for such LED arrays is lacking. This paper reports on near-field and farfield laboratory experiments using an array of two and five narrow-beam LEDs. A near-field approach makes discussions to determine the far-field photometric distance superfluous and leads to correct illuminances at any location with respect to the array, irrespective of the dimensions of the array and the beam angle of the individual components. Introducing the near-field representation of light sources in lighting design offers more accurate predictions when luminaires based on LED arrays with focusing optics are involved.

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Section: Apparent Luminous Intensity Off the Optical Axis Of A Two-lesupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Near-field and far-field goniophotometry of narrow-beam LED arrays

Jacobs

Forment

Rombauts

et al. 2014

Lighting Research & Technology

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“…Over the last few years the notion that the radiance distribution of an extended source could be 7,8,9 projected onto a sphere surrounding the body (rendering the intersection problem trivial), 10,11 and stored as a set of coefficients from an expansion in orthogonal polynomials (solving the storage problem), began to appear. Levin's presentation of this idea was in the form of brief observation; the others that reported actually working on the idea tended to use inconvenient interpolation or data compression schemes.…”

Section: Raytracingmentioning

confidence: 99%

“…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%

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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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Calculations and Measurements

Bommel¹

2019

Interior Lighting

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On Near-Field Photometry

Cited by 16 publications

References 0 publications

Near-field and far-field goniophotometry of narrow-beam LED arrays

Near-field and far-field goniophotometry of narrow-beam LED arrays

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

Calculations and Measurements

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