The world’s biggest authority on light and proper lighting is the InternationalCommission on Illumination (CIE, Commission Internationale de l’Eclairage), which, among other things, publishes documentssummarising the latest knowledgeon light and makes recommendations for the lighting industry on the basis of this knowledge. The CIE’s main document is the so-called Position Paper, summarising the current state of knowledge about light and its effects. The current paper makes recommendations for the development and selection of technologies for interior lighting with regard to its biological non-image forming effects through its spectral composition and the resulting relationship to human health.
The CIE is a scientific institution whose publications are less accessible to non-scientific audiences. However, the Commission’s conclusions are useful for anyone who is involved in lighting, its installation and use, and wants to use light to benefit their own health and that of their neighbours. Below we summarise the main findings of the latest version of the Position Paper from August 2024, and because we couldn’t do that without using a couple of acronyms and terms, we also include a small glossary.
Glossary
Photosensitive
light sensitive, sensitive to light
ipRGC
Intrinsically photosensitive retinal ganglion cells
intrinsically photosensitive retinal ganglion cells
Melanopsin
photosensitive protein dye of light-sensitive ganglion cells, its spectral sensitivity is highest in the blue and cyan regions
integrative lighting
lighting specifically aimed at integrating the visual and non-visual effects of light
ILL response
ipRGC influenced light response; non-visual response to light
Melanopic EDI
Melanopic Equivalent Daylight Luminance; Melanopic EDI
The value indicates how much a light source affects the non-visual system of humans through spectral composition, including our circadian rhythm. The metric indicates how much daylight is needed to achieve the same impact on the organism compared to the measured lighting setting.
Conclusions of the CIE paper
- The photoreceptors of the retina not only enable vision, but are also connected to various sites in the brain through which the spectral composition and intensity of light induce biological effects that strongly regulate human health, performance and well-being.
- The eye not only has conventional vision receptors (rods and cones), but also non-visual photoreceptors, called intrinsic photosensitive retinal ganglion cells (ipRGCs). Their photosensitivity is based on the photopigment melanopsin.
- Light is the main synchroniser of the human biological clock.
- Prolonged exposure to light can improve alertness, affect thermoregulation and alleviate depression.
- Light in the evening and at night can disrupt sleep and suppress the night-time release of the hormone melatonin.
- ‘Integrative lighting’ = the official term for lighting that is specifically aimed at integrating visual and non-visual effects, and which produces physiological and psychological effects on humans.
- However, lighting still erroneously focuses mainly on visual aspects and energy efficiency. Non-visual responses (ipRGC influenced light/IIL responses) are neglected.
- Numerous products designed to affect IIL neglect the overall quality of lighting and its spectral composition, which can compromise human health and well-being.
The CIE recommends:
‘Light hygiene’
- During the day – more is more: minimum exposure of 250 melanopic EDI lux. Very high exposure to full spectral light (= very high melanopic EDI) during the day promotes circadian rhythm, alertness and good sleep.
- Less is more before bedtime: maximum exposure of 10 melanopic EDI lux in the evening for three hours before bedtime. Low melanopic EDI (in the order of 1/25 or less of daytime exposure) in the evening facilitates sleep initiation and consolidation.
- Sleep in the dark: Exposure should not exceed 1 melanopic EDI lux during sleep.
Darkness (very low melanopic EDI, i.e., almost none) at night promotes a strong circadian rhythm and sleep quality, with consequent benefits for daytime performance and well-being.
- Do you work during the night? Goeasy on the light: For activities that require night vision: 10 melanopic EDI lux maximum
- Being outdoors is good for us: Spending the day outdoors contributes to better health and well-being. Light makes a significant contribution to this.
- Let the light in! The CIE recommends not to restrict daylight indoors. (Explain this to your offspring at the computer!)
Important: The recommended values are based on the average values for a healthy population. Individual need varies according to age, health, activity and other factors.
Do you measure light values? Measure them correctly!
- Judge light values and quality using the plane of the eye. In practice, this means that a spectrometer placed on a table gives values that are fundamentally different from the eye of a sitting/standing person looking forward
- Use melanopic EDI luxvalues to describe the non-visual stimuli provided to ipRG cells.
- The comprehensive characterisation of the illuminated environment also includes horizontal luminance, vertical and horizontal brightness, colour quality and other indices to describe the stimulus provided to the visual system.
