Traceability of near-field goniophotometers to the SI units
Vztah goniofotometrů blízkého pole k jednotkám SI
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Goniophotometry is one of the basic photometric measurements in lighting engineering. Aim is to measure spatial characteristics of luminous parts of the luminaires and light sources represented by luminous intensity distribution curve which is needed for lighting computation at level of the preparation of lighting design. Near-field goniophotometry is still a forthcoming technology widely used in photometric laboratories all over the world. Due to compact design of these systems the laboratory space can be saved and they can be installed in a room of usual dimensions because they do not obey the inverse square law from point of view of the whole dimension of the luminaire. The principle of these goniophotometers of the luminance distribution is measurement of luminous part of the luminaires and light sources. By integration over solid angle from this fundamental photometric quantity luminous intensity in particular direction in the space represented by two angles depending on measurement planes is derived. Although theoretical principle and physical model is well-known and defined, in practical realisation of this system some problems occur. One of the problems is traceability to SI units. This fact disqualifies near-field goniophotometer in standards relating to goniophotometry. The methods to prove that near-field goniophotometer works are mostly based on computer simulations compared with practical measurements. But in the practice, appropriate calibration method with traceability to the SI units is still not available, unlike it is clearly used for farfield goniophotometers. The paper describes possibility of the calibration of near-field goniophotometers to SI units by standards which should provide fully traceable calibration to the base. Also method of validation of near-field goniophotometric systems is still opened question for future work. At the present, further works continue on the method of validation in the framework of that CIE Division 2 but this topic is out of scope of this Paper.
Document typePeer reviewed
Document versionFinal PDF
SourceProceedings of the 21st International Conference LIGHT SVĚTLO 2015. s. 245-248. ISBN 978-80-214-5244-2
- Light Světlo 2015