The United Nations has proclaimed 2015 as the International Year of Light and Light-based Technologies (IYL 2015) to “highlight to the citizens of the world the importance of light and optical technologies in their lives, for their futures, and for the development of society.”
In celebration of IYL 2015, the National Research Council of Canada (NRC) has dedicated the month of May to recognizing the importance of “light for quality standards”. The theme is in line with this year’s focus for World Metrology Day: Measurements and Light.
The term ‘quality standards’ conveys ideas of high accuracy (via standards that are traceable to the International System of Units – SI) and reliability (through the development of quality system procedures and demonstration of technical competence from international measurement comparisons) which are the essence of NRC Measurement Science and Standards. NRC’s physical metrology disciplines use optical methods to develop, maintain, improve and disseminate standards for characteristics including whiteness, photometry, radiometry and radiation thermometry, and colour quality.
Light to establish whiteness standards
White means big money in the pulp and paper industry. The “whiteness” of paper is a key component of its market value. NRC, which is recognized as the world authority in paper whiteness measurements, developed the reference instrument that establishes the absolute whiteness level for various types of paper. For almost two decades, NRC has been the world’s keeper of optical property standards for fluorescently-whitened paper as set by the International Organization for Standardization (ISO). Paper companies around the world trace their whiteness measurements back to ISO-authorized labs such as FPInnovations in Canada, and these labs in turn trace their standards back to the measurement science labs at NRC.
NRC works with FPInnovations and the other four ISO-authorized laboratories in the U.S., Sweden, Finland and France to make sure companies around the world have access to the highest quality standards for paper whiteness. NRC and FPInnovations are also working with the International Commission on Illumination (CIE) to improve the lab methods used to measure whiteness of paper. This will benefit not only the paper industry but a wide variety of other manufactured white products that contain fluorescent-whiteners, such as fabrics, laundry detergents, soaps, plastics and cosmetics.
Canada’s ultimate light ruler for photometric, radiometric and radiation thermometry standards
Measuring ultraviolet (UV) light is critical for a wide range of environmental and health issues, emerging industrial technologies, and regulatory requirements pertaining to global trade. NRC’s ultra-high temperature blackbody is one of the world’s most accurate ways to measure UV light. A blackbody is a perfect emitter, so when it is heated, at any particular temperature, it emits a distinct amount of energy at each wavelength of light. Thus, if you know the blackbody’s temperature, you can use a physics calculation to determine the amount of light being emitted at any wavelength.
The state-of-the-art equipment, built in Russia and installed in part by two technicians from Russia’s National Metrology Institute in Moscow, addresses a growing Canadian demand for more accurate UV measurements. In order to deliver these measurements, UV lamps must be calibrated against a known source. This is where the high-temperature blackbody comes in. Its known UV radiation is used to calibrate NRC UV standards, which will then be used by NRC staff to calibrate commercial UV equipment.
Along with improving the ability to measure in the UV range, the high-temperature blackbody improves the accuracy of NRC light measurements for a wide variety of photometric and radiometric applications over the entire optical wavelength range.
The core of the high-temperature blackbody is a hollow tube of a form of graphite that can withstand intense heating. In order to produce the required UV radiation, the graphite core is heated to approximately 3230 ºC, a temperature at which almost all metals melt. The graphite is gradually heated over the course of several hours by running an electrical current through it. The graphite core is insulated with many concentric layers of carbon cloth which are water-cooled.
At 3230 ºC any oxygen would react instantly with the graphite, causing a fire. So, during operation the entire core is flushed with argon, a non-reactive gas. At operating temperature, the high-temperature blackbody produces an intense beam of light that’s emitted from a tiny eight millimetre hole. The energy of this wavelength of light is measured to determine the temperature within the blackbody.
The NRC high-temperature blackbody source is also being used to calibrate NRC primary radiation standards (pyrometers) for use in high-temperature metrology. NRC is participating in an international collaborative effort to investigate the reproducibility of the plateau temperatures of a series of high-temperature metal-carbon and metal-carbide-carbon eutectics. Specialized fixed-point blackbody sources are used as furnaces for preparing these eutectics and the NRC high-temperature blackbody is being used as a reference source to calibrate the NRC optical pyrometer for measuring the temperature of these eutectics. Eutectic-phase transitions are being considered for use as fixed points in future temperature scales, where light-based radiation thermometry methods will provide a high-temperature radiation scale (1000 °C and above). This will ultimately improve the extrapolation of the International Temperature Scale of 1990, ITS-90, which is defined in terms of fixed points of a series of pure materials.
Light to enhance the quality of colours
A decade ago, NRC developed a leading-edge gonioreflectometer — a highly sensitive instrument that can rapidly measure, in three dimensions, the reflectance properties of materials with a variety of colour attributes and surface characteristics. This benefits manufacturers of iridescent paints that reflect a range of hues and exhibit different surface texture or other spatial effects, when light hits them from different angles.
A gonioreflectometer consists of a light source illuminating the material to be measured and a sensor that captures the light reflected from that material as it rotates around a hemisphere. The rotation of the light source and the sensor around the target material is what allows for reflectance to be measured in 3D.
Cosmetics, cars, appliances, clothing and high-end packaging are some of the products for which the proper management of colour and appearance are critical for commercial success. NRC’s capacity to accurately measure 3D reflectance also serves other interests, such as anti-counterfeiting, remote sensing, cultural heritage and medical imaging applications, or the production of new geometry-sensitive materials, such as special effect pigments.
NRC works with national metrology institutes around the world to maintain the global standards that are critical for international trade — everything from time, length and mass to novel measurements needed for medicine, nanotechnology and biotechnology. Light is just one of many tools at NRC metrologists’ disposal to determine and measure compliance to these important quality standards, helping Canadian industry to de-risk product development and add significant value to a wide variety of products.
Originally published as “NRC celebrates ‘Year of Light’” in Spring edition of NCSLI Metrologist magazine, available here.
Joanne Zwinkels (main contributor to the article) is a Principal Research Officer at the National Research Council of Canada (NRC). She received her PhD in Physical Chemistry from the University of Alberta (1983) with specialization in the infrared optical properties of solids. Her research activities involve the development of new reference instrumentation, standards and procedures for high-accuracy spectrophotometry, spectrofluorimetry and color and appearance measurements. Dr. Zwinkels is actively involved in international standardization activities and currently serves as Chair of the Strategic Planning Working Group of the Consultative Committee of Photometry and Radiometry, International Convenor of ISO TC6/WG3 (Paper, board and pulps: optical properties), and Associate Director of CIE Division 2 (Physical Measurement of Light and Radiation).