Work Package 3

WP leader: MIKES

WP 3: Fluorescence

The aim of this work package is to develop traceable facilities, methods, and reference materials that can be used to improve the uncertainties of appearance measurements of surfaces with fluorescent materials.

Most of the existing methods and standards for measuring diffuse reflectance have evolved for non-fluorescent materials with the assumption of their near-Lambertian behaviour. However, for application to a wide variety of materials used in industry at present, the standard spectrophotometric measurement techniques are inadequate. This has led some industries to purchase and use similar “conventional” devices in order to avoid inter-laboratory disagreements. As a result there is an ad-hoc de-facto standard implemented by end-users, which is preventing the instrument industry from developing new, instrumentation which is able to fulfil the requirements of end users. In addition, there are concerns that current methods and results are not always comparable amongst different branches of industries. For example the fluorescent measurements in paper industry have to be comparable with printing technology, paint industry, and even in display devices technologies. In this work package we propose to carry out five tasks to address the problems of measuring spectral diffuse reflectance of fluorescence surfaces and develop relevant solutions. This will be achieved by introducing improvements in measurement facilities and reference materials and by providing measurement data needed for correlated visual appearance evaluations.

Task 3.1: Tools and techniques for calibration of geometrical parameters of gonio-photometers and fluorometers

Start: September 2013, End: February 2014

The aim of this task is to develop techniques and experimental procedures to ensure reliable and accurate measure of geometric parameters for illumination/observation geometries specified by CIE, ASTM, and ISO and other standardising bodies.

Background: Reliable experimental procedures are needed for calibrating observation angles of spectral diffuse reflectance and colour measurement instruments. Most of colour measuring instruments incorporating goniometers give coordinates for a specific geometry or a multi-angle configuration. For many materials, those coordinates are strongly dependent on the illumination/observation geometry, but this geometry cannot be calibrated once the instrument has been manufactured.

Description of work: CSIC with support of MIKES and REG(UA) will develop the tools and techniques enabling the calibration of the illumination/observation geometry.

Task 3.2: Validation and traceability of facilities for surface fluorescence standards

Start: March 2014, End: August 2014

The main aim of this task is to characterise existing measurement facilities of workpackage JRP-Partners (MIKES, CSIC, INRIM), and REG(UA) to strengthen the traceability of fluorescence measurements of diffuse reflectance standards and to reduce the uncertainty of the measurement to below 0.5%. One of the objectives of this work is to validate each facility for a unique measurement geometry and/or method.

Description of work: The validation will be provided via an inter-laboratory comparison of these facilities. The goniofluorometer of MIKES will be employed as the pilot facility to provide traceability to most of the measurement geometries and wavelength range of 250 nm -900 nm. To reach the objectives of this task MIKES with support from CSIC and REG(UA) will develop the tools necessary for the validation of spectrophotometers and fluorometers at the 0.2%-level. In particular, the major contributions to the uncertainty budget of surface fluorescence measurements will be investigated and minimised to go beyond the state-of-the-art of spectrophotometry and spectrofluorometry

Task 3.3: Assessment of fluorescent diffuse reflectance standard materials

Start: December 2013, End: November 2015

The aim of this task is to identify and study several types of reference artefacts needed for calibration and characterisation of instruments used for measuring fluorescence diffuse reflectance materials.

Background: Today, most measurement facilities capable of absolute fluorescence measurements apply fixed measurement geometry and rely on the assumption of Lambertian emission of fluorescence from liquids and solid amorphous material. Angular resolved reflection data are becoming more relevant to industry due to advanced production methods. They are an important reference for manufacturers, providers and users of radiometric and photometric products. As an example, the printing industries need stable and robust reference materials suitable for standard illuminant D50 and standard colorimetric observer 2° field of view. The reference material is preferred to have an optical indicatrix and bispectral characteristics of fluorescent papers.

Description of work: A plan for the selection, preparation and characterisation of the required materials will involve consultation between the stakeholders and JRP-Partners and REGs. Two rounds will be devoted for the selection of final artefacts. The materials to be studied include a synthetic variant of Calcium Tungstate known as Scheelite with typically bright blue fluorescence applied to ceramic tiles. In this task four samples of custom designed UV-activated chromatic and PTFE materials will be thoroughly characterised for their emission and scattering characteristics using a fluorometer and a reference goniofluorometer at MIKES.

The objectives of the task will go beyond the state of the art by improving the 1% uncertainties to as low as 0.2 % – 0.5 % in the measurement of luminescent radiance factor of fluorescence standards. The task will strive to offer material standards to the relevant industrial stakeholders, which have near-Lambertian emission and scattering behaviour with radiance factors of 0.9 – 1.1 for a wide angular range.

Task 3.4: Combined effect of translucency, gloss, and fluorescence in standard artefacts

Start: December 2014, End: April 2016

The aim of this task is to improve the understanding of translucency and gloss effects in the standard artefacts needed for calibration and characterisation of instruments used for measuring diffuse reflectance and transmittance of materials.

Background: One problem in manufacturing of fluorescent diffuse reflectance standards is the translucency of diffusing materials. In addition to the desired diffuse reflectance/transmittance, there is a specular/refracted component in the reflected/transmitted beam. Diffuser materials show varying translucency with process or material, sometimes even when the trade name is the same [42].

Description of work: In this task, UV activated diffuser materials will be selected and purchased. Thin sheets with varying thickness and glossiness will be produced from the materials, and the reflection and transmission profiles of the sheets will be measured with a goniospectrometer/gonioreflectometer as a function of wavelength and angle of incidence (over black , white, and free space). The materials and the gathered information are then shared with WP4 and other participants in WP5 to further investigate the interrelationship of these effects in the colour and other appearance measurands. The standards fabricated in Task 3.3 will be also tested for the level of translucency to evaluate the effect of translucency on the performance of the fluorescence artefacts.

Task 3.5: Need of fluorescent colour standards for the “gaps” in the gamut

Start: March 2015, End: August 2016

The aim of this task is to identify potential needs of new colour standards.

Description of work: Within this task specific colour gamut of current fluorescent materials and standards, in or out of the Rösch-MacAdam colour solid will be characterised. Based on this study, the project will propose to stakeholders the generation of new reproducible and feasible fluorescent standards for covering empty/blank regions in and out the classical colour solid . When an industrial need appears, the selection of hue, chroma and lightness of the new standards to be manufactured will be carried out taking into account the ISO database from the ISO 12640 normative. Finally, the identified colour standards will be fabricated.