Abstract Application of Cone Fundamentals in Photometry

In 2024 we will celebrate 100 years since the publication of the spectral luminous efficiency function for photopic vision, V(l), adopted by the CIE as the function that links the photometric and radiometric systems.  Since then, other than for some specialised applications, all photometers (illuminance meters and luminance meters) are designed to have a spectral responsivity that matches the V(l) function.  However, it is also well known that V(l) is not a perfect match to human vision, and in particular it underestimates the visual response in the blue region.

In 2006 and 2015, the CIE issued two key technical reports [1][2] that describe the human perception of colour in physiological terms, taking into account the spectral response of the long-wave (L-), medium-wave (M-) and short-wave (S-) sensitive cones and correcting for the spectral absorbance of the other parts of the eye that transmit the light before it reaches the cones.  These are referred to as “cone fundamentals”.  In particular, the 2015 publication includes a cone-fundamental-based spectral luminous efficiency function, VF(l), which is a more accurate match to human vision than the V(l) function.

However, the situation is more complicated than simply redefining photometry in terms of the VF(l) function.  The VF(l) function is still just a single function, whereas human vision has a large diversity in parameters such as the age of the observer, the field of view, photopigment type, and life factors.  Furthermore, simply requiring a change of photometer design to the VF(l) function may result in a worldwide upheaval taking a generation to transition!

In 2023, CIE established a research forum, RF-05 Implementation of CIE 2006 Cone Fundamentals in Photometric and Colorimetric Measurements, chaired by Tony Bergen (AU).  The purpose of the RF is to engage all stakeholders (research institutes, laboratories, instrument manufacturers, lighting manufacturers, NMIs, industry, etc.) to consider the impact of cone fundamentals on measurement of fundamental quantities.

This presentation will outline the basics of cone fundamentals and discuss the implications of the adoption of cone-fundamental-based photometry.

References

[1] CIE 170-1:2006, Fundamental Chromaticity Diagram with Physiological Axes — Part 1

[2] CIE 170-2:2015, Fundamental Chromaticity Diagram with Physiological Axes — Part 2: Spectral Luminous Efficiency Functions and Chromaticity Diagram.

Tony Bergen is Vice-President Technical of the International Commission on Illumination (CIE) and President of CIE Australia, the Australian National Committee of the CIE.  He is a physicist who has been working in the field of light, lighting and its measurement for over 25 years.  Prior to becoming Vice-President Technical, Tony was Director of CIE Division 2, the Division of the CIE that deals with the physical measurement of light and radiation.  He has been a co-author of over 20 CIE publications, serves as chair of two CIE Technical Committees, and serves as chair of the CIE Research Forum RF-05 Implementation of CIE 2006 Cone Fundamentals in Photometric and Colorimetric Measurements.