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Review
. 2023 Mar 17;5(1):116-140.
doi: 10.3390/clockssleep5010012.

Light as a Modulator of Non-Image-Forming Brain Functions-Positive and Negative Impacts of Increasing Light Availability

Islay Campbell  1 , Roya Sharifpour  1 , Gilles Vandewalle  1
Affiliations
Review

Light as a Modulator of Non-Image-Forming Brain Functions-Positive and Negative Impacts of Increasing Light Availability

Islay Campbell et al. Clocks Sleep. .

Abstract

Light use is rising steeply, mainly because of the advent of light-emitting diode (LED) devices. LEDs are frequently blue-enriched light sources and may have different impacts on the non-image forming (NIF) system, which is maximally sensitive to blue-wavelength light. Most importantly, the timing of LED device use is widespread, leading to novel light exposure patterns on the NIF system. The goal of this narrative review is to discuss the multiple aspects that we think should be accounted for when attempting to predict how this situation will affect the NIF impact of light on brain functions. We first cover both the image-forming and NIF pathways of the brain. We then detail our current understanding of the impact of light on human cognition, sleep, alertness, and mood. Finally, we discuss questions concerning the adoption of LED lighting and screens, which offer new opportunities to improve well-being, but also raise concerns about increasing light exposure, which may be detrimental to health, particularly in the evening.

Keywords: ageing; blue light; circadian rhythms; cognition; functional magnetic resonance imaging; intrinsically photosensitive retinal ganglion cells; melanopsin; non-image forming; sleep; teenagers.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Photoreceptor sensitivities and light spectra. (A) Spectrum of white LED, fluorescent, and incandescent light sources and natural daylight. (B) Spectral sensitivities of retinal photoreceptors in primates. (C) Wiring and position of retinal photoreceptors. ipRGCs: intrinsically photosensitive retinal ganglion cells expressing melanopsin. RGC: retinal ganglion cells. Reproduced and adapted with permission from [14].
Figure 2
Figure 2
Schematic of main ipRGC projections in mice. Adapted with permission from [44,48]. Information from [36,44,46,48]. Numbers of the scheme correspond to numbers in the adjacent table. Coloured dots correspond to known projection of ipRGCs subtypes in rodents (M1 to M6).
Figure 3
Figure 3
Light’s impact image forming (IF) and non-image forming (NIF) pathways. (A) Light signal reaches the central nervous system via the retinohypothalamic and optic tracts of the optic nerve to affect IF and NIF functions. Light impact on NIF functions depends on light factors and individual factors. (B) The industrial concept of integrative lighting aims to design individually tailored dynamic lighting accounting for visual perception and acuity, together with light’s impact on NIF functions, including mood, circadian rhythms, productivity (i.e., attention/alertness), and environmental sustainability. NIF’s consideration of integrative lighting largely lacks a strong scientific basis.
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Grants and funding

I.C. and G.V. are supported by the Fonds National de la Recherche Scientifique (FRS-FNRS; Research credit–CDR and FRIA bursary). R.S. and G.V. are supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 860613 (LIGHTCAP project). All three researchers are further supported by the ULiège-Valeo Innovation Chair “Health and Well-Being in Transport” and Sanfran (LIGHT-CABIN project), ULiège and Leon Fredricq Foundation.

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