1,720,984 research outputs found
Detector based calibration for illuminance and luminance meters - experimental results
No full textThe connection between illuminance and luminance measurements is considered to create a traceability link among a highly accurate illuminance meter, which is considered as an internal standard of the Photometric Laboratory, University of Padova, Padova, Italy, and other illuminance meters or photometric heads and luminance meters. After an introduction on the main involved definitions and equations linking the illuminance and the luminance measurements, this paper presents the instruments to which the procedures are applied and, at the end, results regarding the absolute calibration of the instruments under test, the check of their linearity, and the analysis of their spectral responsivity within the visible range. Following this way, this paper shows the main results in the connection among instruments devoted specifically to illuminance and luminance measurements. Then, it also introduces a comparison to other photometric heads, e.g., sensors that are part of more complex systems, like an integrating sphere for luminous flux measurement. In this last case, it has no significance to evaluate the difference between the absolute outputs, but it is interesting to compare the response of the two devices considering their linearity and their relative spectral response. A special section devoted to the evaluation of the spectral response presents a new simple but effective method. The application of a detector-based method allows a significant reduction of the uncertainty in the internal calibration of the photometric instruments, granting the continuity of the Photometric Laboratory operation contemporarily
Analysis of the Performance of a Goniometer for Studying Surface Reflection
No full textAn accurate goniometer was constructed, being a part of a system that is designed for the measurement of reflecting properties of surfaces. It can be used to orient a surface of the sample under test arbitrarily with respect to the observing direction and the direction of the shooting light beam. The high performance (revolution angle uncertainty equal to 0.1deg), which is required as a specification for the construction, is checked. Particular attention has been given to analyzing the orthogonality among the revolution axes of each goniometer component and their convergence in the goniometer center. The linearity error of each revolution motion has been measured by using a differential method, which proves to be effective in highlighting the small linearity deviation and verifying the uncertainty declared by the manufacturer
Comparison of Luminance Measurement based on Illuminance and Luminance Detectors
No full textThe connection between illuminance and luminance measurements is considered to create a traceability link among an highly accurate illuminance meter, considered as an internal standard of the Photometric Laboratory of the University of Padova, and other illuminance meters or photometric heads and luminance meters. Examples are presented in the paper. The application of a detector-based method allows a significant reduction of the uncertainty in the internal calibration of the photometric instruments, granting the continuity of the Laboratory operation, contemporarily
Illuminance from Luminance Measurement Experimental Results
No full textThe ability of multi luminance meters in identifying the directionality of light sources and their possibility in selecting and analysing the contribution to luminance of sources located in different places, makes the Photometric Laboratory of the University of Padova to use them to measure illuminance in critical cases, like in glare quantification and measuring of reflection properties of surfaces. After a description of the method and the presentation of some specific applications, measurement results are presented, showing the efficacy of the proposed method by comparing measurement obtained by illuminance meters and by the use of a multi luminance meter
A simplified approach to the assessment of photobiological safety of LED sources
No full textThe radiation from a light source could have many desired effect, but, as all forms of energy, it modifies the material it reaches. Limits are defined by standards to protect human skin eye and retina also against radiation intended for general lighting service. A brief description of the approach identified by the standard is here reported. It requires pretty sophisticated instrument to measure the involved quantities. This work shows the possibility of using instruments usually present in a photometric laboratory, like illuminance meter and radiometers, to approach the issue identified in the standards, at least in some simpler situations, as in the case of LED based light sources. The assured uncertainties are worst than the ones obtainable by following the acknowledged track, but they are small enough to allow to associate the light source with a worst case risk group
Internal Traceability between Luminous Flux and Illuminance Standards
No full textTwo methods for the measurement of the luminous flux are presented: the first is based on an integrating sphere and a luminous flux standard lamp, the second utilizes an accurate goniometer and an accurate illuminance meter. A comparison between the two methods is carried on for two different light sources: an LED and a halogen source, presenting different luminous fluxes. The measuring procedure and an evaluation of the measurement uncertainties are described for both the methods. The comparison shows a good agreement between the two measuring processes: both of them allow the identification of the luminous fluxes with relative uncertainties of about 1.5%, covering the differences between the luminous flux values. The comparison is considered a valid possibility of verifying the calibration constancy of the laboratory luminous flux and illuminance standards
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