A practical method of comparing luminous intensity distributions

Bergen, A. S. J.

doi:10.1177/1477153511435769

Cited by 20 publications

(15 citation statements)

References 2 publications

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“…For applications in the comparison of gonio-photometric measurements of luminaires assuming identical instrumentation, a range of 98% to 99% is considered good and 99% to 100% very good [38]. When different instruments or computational methods are employed, a lower degree of accordance can be expected.…”

Section: Comparison Of the Results Of The Extended Matrix Formalism Amentioning

confidence: 99%

Computational Combination of the Optical Properties of Fenestration Layers at High Directional Resolution

Grobe

2017

Buildings

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Abstract:Complex fenestration systems typically comprise co-planar, clear and scattering layers. As there are many ways to combine layers in fenestration systems, a common approach in building simulation is to store optical properties separate for each layer. System properties are then computed employing a fast matrix formalism, often based on a directional basis devised by JHKlems comprising 145 incident and 145 outgoing directions. While this low directional resolution is found sufficient to predict illuminance and solar gains, it is too coarse to replicate the effects of directionality in the generation of imagery. For increased accuracy, a modification of the matrix formalism is proposed. The tensor-tree format of RADIANCE, employing an algorithm subdividing the hemisphere at variable resolutions, replaces the directional basis. The utilization of the tensor-tree with interfaces to simulation software allows sharing and re-use of data. The light scattering properties of two exemplary fenestration systems as computed employing the matrix formalism at variable resolution show good accordance with the results of ray-tracing. Computation times are reduced to 0.4% to 2.5% compared to ray-tracing through co-planar layers. Imagery computed employing the method illustrates the effect of directional resolution. The method is supposed to foster research in the field of daylighting, as well as applications in planning and design.

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Section: Comparison Of the Results Of The Extended Matrix Formalism Amentioning

confidence: 99%

Computational Combination of the Optical Properties of Fenestration Layers at High Directional Resolution

Grobe

2017

Buildings

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“…The level of global accordance of f A,B 84% and f RB = 92% is low compared to results that are referred as "good" ( 98%) or "very good" ( 99%) in the literature [24]. This rating is related to a comparison of measurements of the same luminaires with identical goniophotometers, but the results for the reference beams f RB = 92% are expected to be in this range.…”

Section: Discussionmentioning

confidence: 99%

“…Among the existing metrics for global accordance over the hemispherical distribution [22,23], a quality index is proposed for applications in the characterization of light sources [24]:…”

Section: Comparison Metrics For Directionally Resolved Bsdfmentioning

confidence: 99%

Accordance of Light Scattering from Design and De-Facto Variants of a Daylight Redirecting Component

Noback¹,

Grobe²,

Wittkopf³

2016

Buildings

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Abstract:For the systematic development of a small-scale daylight-redirecting louver system the impact of manufacturing on light scattering characteristics has to be quantified, localized and understood. In this research, the accordance of the measured scattering distributions of a de-facto production sample V1 with the computed predictions based on its design geometry V2 are quantified for selected incident light directions. A metric describing the global accordance of distributions is adapted to quantify their overall difference. A novel metric of local accordance allows further analysis. A particular low global accordance between V1 and V2 is found for an incident elevationTo test the hypothesis that this result can be explained by observed geometric deviations, a simulation model V3 replicating these is compared to the design. The hypothesis is supported by the resulting high degree of accordance. The low local accordance for individual outgoing light directions indicates geometric non-uniformity of the sample V1. This method has been found useful for product development and quality assurance. Beyond their application in the proposed method, global and local accordance have potential applications in all fields of light scattering measurements.

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“…Inserting equations (11)-(13) into (10), the apparent intensity on its optical axis is found for the LED array, focused at a distance F from the photometric center ( ) Figure 3 displays these theoretical apparent intensities for a 2LED array using equations (14), (15) and the following parameters:…”

Section: The Apparent Intensity Of Focused Led Arraysmentioning

confidence: 99%

Near-field and far-field goniophotometry of focused LED arrays

et al. 2014

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Luminaires are conventionally modeled using a far-field representation. To calculate this representation, a photometer revolves a light source at fixed distance and illuminances are measured in a set of angular directions. Using the inversesquare-law, the far-field intensity, also termed luminous intensity distribution is then calculated. For Lambertian sources, the far-field starts from a distance of five times the maximal dimension of a light source; which is called the limiting photometric distance. The advent of luminaires composed of LED arrays with narrow beams have shown that this limit is no longer valid and far larger distances (up to 15 times the maximal diameter) are suggested by the lighting community. This problem is even more outspoken when the individual LEDs are focused at close distance, as in e.g. surgical luminaires. To overcome these problems, we exploit the use of a near-field representation to describe an array of two narrow-beam LEDs focused at close distance. For such a test source, this paper shows how a near-field luminance goniometer is able to construct ray-data. Ray files can be used to calculate a near-field representation and far-field representation of a light source. These measurements are validated by a theoretical derivation of the intensity of an array, using a simple analytical model to describe the emission of the individual LEDs. This near-field approach makes discussions to determine the far-field photometric distance superfluous.

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A practical method of comparing luminous intensity distributions

Cited by 20 publications

References 2 publications

Computational Combination of the Optical Properties of Fenestration Layers at High Directional Resolution

Computational Combination of the Optical Properties of Fenestration Layers at High Directional Resolution

Accordance of Light Scattering from Design and De-Facto Variants of a Daylight Redirecting Component

Near-field and far-field goniophotometry of focused LED arrays

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