Light is the main synchronizer of the human biological clock. It can shift the phase of the circadian rhythm and can regulate the timing and quality of our sleep. Light in the evening and at night can be disruptive for sleep and cause acute suppression of the nocturnal release of the hormone melatonin. There are also reports that light can increase heart rate, improve alertness, alleviate seasonal and non-seasonal depression, influence thermoregulation, and affect the electroencephalogram (EEG) spectrum. Exposure to light elicits fast responses (i.e. in the range of milliseconds and seconds) in the pupillary reflex or in brain activity. Lighting standards, regulations and practice often focus on visual and energy efficiency aspects of light and do not address non-image-forming (NIF) responses to light. This can result in lighting conditions that compromise human well-being, health and functioning.
The above-mentioned biological effects of light are elicited by stimulation of ocular photoreceptors. The classical receptors for vision, the rods and cones, are relatively well understood and characterized by existing CIE publications. Pioneering work over the last 25 years revealed that the eye has another kind of photoreceptor. This photoreceptor plays an important role in non-visual effects of light and has a peak sensitivity in the shorter wavelength part of the visible spectrum. Such photoreceptors are known as intrinsically-photosensitive retinal ganglion cells (ipRGCs), and their intrinsic photosensitivity is based on the photopigment melanopsin that is contained within them.
For non-image-forming effects of light, a description of optical radiation solely according to the photopic action spectrum is not sufficient. Moreover, there is no single action spectrum for non-visual responses. The actual NIF effects due to ocular exposure to light depend on the combined responses of all photoreceptors and there is good evidence for the potential for all receptor types to contribute to these responses.
The International Standard CIE S 026/E:2018 defines spectral sensitivity functions, quantities and metrics to describe the ability of optical radiation to stimulate each of the five photoreceptor types that can contribute, via the melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs), to retina-mediated non-visual effects of light in humans. The document is applicable to visible optical radiation in the wavelength range from 380 nm to 780 nm. In addition, the document includes information concerning the effects of age and field of view (FOV) when quantifying retinal photoreceptor stimulation for ipRGC-influenced responses to light (IIL responses).
The document does not give complete information for particular lighting applications, or for the quantitative prediction of IIL responses. The document is not intended for colorimetric contexts, nor does it address health or safety issues such as those resulting from light treatment, flicker or photobiological safety and only relates to retinal photoreception. Tables of the data of the action spectra of the five photoreceptor types defined in this document are made electronically available for purchasers of this publication via a respective download link.
This CIE International Standard has been prepared by Joint Technical Committee (JTC) 9 “CIE system for metrology of ipRGC influenced light response” of Division 1 "Vision and Colour", Division 2 "Physical Measurement of Light and Radiation", Division 3 "Interior Environment and Lighting Design", and Division 6 "Photobiology and Photochemistry" of the Commission Internationale de l’Eclairage, under lead of Division 6. It has been approved by the CIE National Committees. It is readily available at the National Committees of the CIE or via the CIE Webshop.
This publication is also available in Chinese.
A report of a workshop held at the 29th Session of the CIE, a Toolbox and a User Guide supporting the content of the standard are available from the links below.
CIE S 026 Toolbox (v1.49a - November 2020)