Alessandro Scroccaro

Detector-Based Calibration for Illuminance and Luminance Meters—Experimental Results

The 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.

Comparison of luminance measurement based on illuminance and luminance detectors

The 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.

Internal Traceability between Luminous Flux and Illuminance Standards

Two 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.

On the use of broadband ultraviolet detector calibration

Measurement of ultraviolet radiation is a common issue in many fields of applications. The easy way to approach to ultraviolet measurement is by using broad band probes. Their use should be straightforward, but their calibration is not always simple to be applied in small industrial, test and research laboratories. The paper presents the two main approaches to the calibration of ultraviolet probes, with their related limitation on their use and difficulties in the extension of the calibration to the cases considering radiating source different from the one used in the calibration. Starting from the approach applied at metrological laboratories, an attempt to overcome this problem is presented which takes advantage of the information commonly provided by manufacturer on data sheets of probes and sources, i.e. data easily achievable by all laboratories.

A multispectral imaging device for monitoring of colour in art works

In the present work, a new imaging device for multi spectral analysis in the visible range is presented, together with its own performances and an example of its application. The instruments can be used to acquire photometric and colorimetric characteristics of wide surfaces in quick and easy way. It is composed by a scientific grade CCD camera and a tunable narrow band filter bench; it acts as a spectroradiometer with a high spatial resolution and a spectral resolution, depending on the bandwidth of the filters. Its application as monitoring device is presented; it is the case of the colour fading analysis of an art print undergone a light forced exposure.

The importance of testing road lighting plants: A simple system for their assessment

Here it is presented a system able to perform automatic measurements, according to national and international standards, of the illuminance and the luminance produced by a road lighting system. Even if it requires the road under analysis is closed, it reduces highly the required time for qualifying a road lighting plant. The description of the system is presented together some exemplifying measurement results carried out on real road lighting system.

The Metrological Characterization of a Goniometer for the Analysis of Surface Properties

An accurate goniometer was constructed being a part of a system devoted to the measurement of reflecting properties of surfaces. By it a surface of the sample under test can be arbitrarily oriented with respect to the observing direction and the direction of the shooting light beam. The high performances (revolution angle uncertainty equal to 0.1deg) required as specifications for the construction are checked. Particular attention is used to analyze the orthogonality among the revolution axes of each goniometer components and their convergence in the goniometer center. The linearity error of each revolution motion is measured by using a differential method. It proves to be effective to highlight the small linearity deviation and to verify the uncertainty declared by the manufacturer

A simplified approach to the assessment of photobiological safety of LED sources

The 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.

Commercial TiO 2 P25 activation: Evaluation of efficacy in photodegration processes of different radiating sources

The paper describes the system, the procedure and the first results of a series of experiments of photocatalytic degradation of organic compounds (phenols and pyridines) carried out using commercial P-25 TiO2 as catalyst and commercial LEDs as light sources. A relevant amount of organic products (more than 50%) is converted to CO2 and aliphatic alcohols and carboxylic acids are formed as intermediates. Typically, in the case of phenols the degradation times are doubled (from 200 to 400 minutes) by comparing the processes performed using LEDs and conventional UV lamps. In the case of pyridines the times are comparable. These preliminary results are aimed to establish the lowest radiation power which can induce titania activation in order to design and optimize suitable cheap devices for pollutant degradation.

Performance analysis of an imaging spectro-chroma meter

The paper considers the possibility of realizing an image spectro-chroma meter by a scientific grade CCD camera and a tunable narrow band filter bench. The presented system allows at recording a multi spectral imaging of the scene, acting as a spectroradiometer with a high spatial resolution and a spectral resolution depending on the bandwidth of the filters. The characterization of the constituting components is briefly described and some evaluations of their performances are presented. In particular, the spectral transmission coefficients of the filters are evaluated together with the power spectral responsivity of the CCD camera. As an example of application, the light reflected by coloured sample is considered and both the spectral radiance and the correspondent colour coordinates are determined. A comparison between measurements obtained by the CCD spectro-chroma meter and by a spectroradiometer allows at quantifying the performance of the new system: for every coloured light, the measured spectral radiance differs less than 2%, so as the luminance value, when a light approximating the Illuminant A is considered. For the same white source, the errors on x and y coordinates are always less 0.002.The system is also used to measure the spectral reflection coefficient of the same coloured samples obtaining performances close to the ones of a good spectroradiometer. The error on spectral reflectivity is about 5% and the error on the CIE 1976 (L*a*b*) coordinates is of the order of ΔE*=3 under the Illuminant A.