New primary standards and traceability for radiometry

Europe is world leading in low energy lighting and optical technologies for communications, healthcare and security, and it makes 30 % of all light  measurement devices in a total global market worth €23 billion.

Standards for light measurement, which were developed for incandescent lighting, use radiometers to measure radiant power to link it to the SI unit of luminous intensity – the candela. Radiometers converting light into electrical power are complex to use and operate at very low temperatures. As light generation technologies develop, new accurate standards are needed for determining the intensity of different light sources, with robust links to the candela, to enable industrial calibration labs to make reliable measurements.

This project developed two new primary standards for radiometry, one that operates at cryogenic temperatures with very high accuracy, and another for use at room temperature that can, for the first time, be easily used by calibration and testing laboratories.

The project:

• Developed silicon photodiodes, which emit a voltage in response to light. These were implemented into two predictable quantum efficiency detector (PQED) devices: a highly accurate low temperature version and a room temperature version
• Increased the accuracy of existing cryogenic radiometers and used these to validate the cryogenic PQED, confirming very low uncertainties and its suitability for comparing light measurement devices to the candela
• Developed a room temperature variant of the PQED, optimised its performance and validated it against the candela through comparisons to the cryostat version
• Used the room temperature PQED to calibrate commonly used industrial sensors with values agreeing to within the 100 ppm uncertainty goal, significantly shortening the traceability chain to the Candela for such devices.

This project enables calibration and testing laboratories, and the industries they serve, to benefit from new light sensor detectors and techniques by providing reliable calibrations with robust links to the SI Candela. The PQED has been accepted, alongside the cryogenic radiometer, as a method to directly compare light measurement instruments to the candela with very low uncertainties. Room temperature PQEDs were shown to be suitable for use in industrial labs with accuracy requirements at the 100 ppm level. A patent application has been filed for the novel photodiodes that were developed in the project which will be commercialised by the newly formed Finnish company, ElFys Oy.

Project research will help the European photo-sensor industry grow its global lead, as applications expand into new areas such as advanced diagnostic devices, healthcare treatments, and smart imaging. This in turn supports Europe’s lighting and optical industries, improving quality control for innovative optical technologies.

EMPIR project 18SIB10 chipS·CALe builds on this work.