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Evaluating Lighting Equipment
Published in Craig DiLouie, Lighting Redesign for Existing Buildings, 2020
Standard LM-79-2008 includes the environmental conditions for testing, how to operate and stabilize the LED sources during testing, and the methods of measurement and types of instruments to be used. It is based on a method called absolute photometry, which simply means that the reported information is directly representative of the speciic product tested and is not derived relative to any rated lamp standard. Essentially, the product is measured using an integrating sphere to measure gross light output and color characteristics, and a goniophotometer, a photometer that measures light intensity reflected from a surface at different angles (traditionally used for conventional luminaires to measure luminous intensity distribution values, but using relative photometry). The combined testing objectively captures 11 aspects of performance including total lumen output, luminaire efficacy, chromaticity(from which color rendering index, or CRI, rating can be derived), and correlated color temperature. Product performance data provided by manufacturers that have tested their products using LM-79 creates needed reliability of information for decision making and comparison.
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
The second method, the goniophotometer, uses a cosine-corrected detector that moves on an imaginary sphere of radius r enclosing the LED. The detector measures the irradiance E as the partial radiant flux dΦ incident on a detector area dA as a function of θ and φ. The angles θ and φ vary from 0° to 360°. The total radiant power Φ is obtained by integrating the irradiance over the entire sphere surface. Alternatively, instead of moving the detector, which requires mechanical adjustments, the LED can be rotated about its tip. The CIE recommended distance LED—detector is 30 cm, the area of the detector should be 1 cm2 in the case of diffuse LEDs, and should be reduced for measurements of narrow-angled LEDs. The goniophotometer provides greater accuracy than the integrating sphere, which includes numerous geometric and spectral sources of error, in particular the wide range of radiation characteristics of LEDs.
Measurements
Published in J. R. Coaton, A. M. Marsden, Lamps and Lighting, 2012
The difference in the type of measurements made with the two pieces of apparatus is that the polar photometer makes measurements of the luminous intensity on a sphere surrounding the luminaire, whereas the goniophotometer measures over a relatively small angular area. Also a goniophotometer measures in small angular increments, but essentially both instruments measure the variation in luminous intensity with angle around the luminaire.
On the average horizontal illuminance in rooms with one or two point light sources
Published in Architectural Science Review, 2023
Rizki A. Mangkuto, Nurul Jamala, Beta Paramita
As a side note, it is likely that the cosine coefficient n of the downlight point source or luminaire is not readily known. Of course, one can opt to perform a goniophotometer measurement of the source luminous intensity distribution (CIE, 1996), from which the coefficient can be derived. In a real-world scenario, with the source already installed and with the occurrence of room surface inter-reflection, the following procedure can be conducted. One shall perform at least three illuminance measurements: (1) EO is the total horizontal illuminance at point O (cf. Figure 1(a)) exactly beneath the source, (2) EO,d is the direct horizontal illuminance at point O; which can be realized by placing a black, narrow band circling the photosensor of the illuminance meter, to block inter-reflected light and (3) EP is the total horizontal illuminance at point P (cf. Figure 1(a)). If the inter-reflected illuminance is assumed constant, one can write:
Thermal Analysis of Light Source for Optogenetics Experiments
Published in IETE Journal of Research, 2020
Rabinder Henry, Velmathi Guruviah
The detected illumination and spectral characteristics are analysed using SpecWin Pro Analyse software [18]. The radiometric parameters irradiance (W/m2), radiation intensity (W/Sr), and photometric parameters luminous intensity (cd), illuminance (lx), colour saturation, and spectral distribution are measured using a Goniophotometer. As shown in Figure 26, the spectral characteristics are determined for a spherical co-ordinate system (radial axis r, theta-axis θ, phi-axis θ) but in the measurements made the parameters are estimated only for the x-axis and y-axis by keeping phi-axis θ at zero.