Effects of light

The biological effect of light is bigger than most people are aware of.

Light has an effect on our biology and wellbeing that is greater than most people are aware of and that goes beyond the visual effects of light. It affects normal human physiology in a profound way such as sleep and growth.

With light we can affect mood, improve sleep and treat depression. But light also has a direct alerting effect and can affect productivity, learning and memory consolidation.

Group of people looking at sunset

It all starts in the eye.

Eye formation begins 22 days into embryonic development, and the eye continues to develop even after birth. In the back of the eye we have the retina which consists of several layers. Outermost are the photoreceptors. Up until around 2000 it was believed to only exist two types of photoreceptors, rods and cones. Recently a third photoreceptor stimulated by its own wavelength of light, separated from that of rods and cones, was discovered.

Furthermore, this receptor was found in the ganglion cell layer and not in the photoreceptor layer of the retina. It contains melanopsin, a photopigment different from that of rods and cones with a spectra around 480 nm. The ganglion cells in the retina form the optic nerve that transport light information to the brain from the eye. Most of the nerve fibres projects to the visual cortex in the back of the brain.

A portion of the nerve fibers coming from the melanopsin-containing ganglion cells project directly on to the hypothalamus and the suprachiasmatic nucleus where light information is used to synchronize the circadian rhythm with our surroundings1,2,3.

Light to promote health

Light has a significant effect on biological functions and our daily routines, and is central to our well-being. Exposure to daylight affects our sleep quality, efficiency, alertness and similar other important factors for our health. Research has led to a number of exciting study results that form the basis of BioCentric Lighting™.

Light to prevent disease

Other effects of light on humans are diseases that demonstrate seasonal and diurnal patterns. Seasonal affective disorder (SAD) and acute myocardial infarction (AMI) are two examples, occurring more frequently during the darker months of the year4,5. Light can have an effect on sleep quality6,7, cognitive performance8 and physical performance9, which in turn may impose long term health risks.

Effects of light depends on



Sleep patterns are directly connected with our circadian rhythm. Research shows that light can correct a disturbed circadian rhythm. The strength of the synchronization depends on the light distribution and on the time of exposure10

Blue light has a direct alerting effect and it can affect our sleep. It is important to reduce exposure to blue light in the evening. By avoiding use of screens late at night, or activating night shift on smart phones and computers, you can limit your exposure.

On the other hand, light, and especially blue-enriched light, in the morning stabilizes the circadian rhythm11.

Man in empty dark office

What is circadian misalignment?

Though we are biologically adapted to spending time outdoors, we spend a majority of our time indoors. Indoor light may not always meet our light exposure needs. Without proper synchronization, the individual cellular clocks work at their own pace causing a misalignment12. Circadian disruption is associated with short and long term health effects.


Mood is related to light exposure. Light which stimulates the circadian system has a direct mood enhancing effect and studies indicate that dawn simulations in the morning improve the subjective perception of well-being6,13.


The importance of adequate lighting in schools and its effect on well-being is important to reduce children’s level of stress. A group of Swedish researchers have argued for better lighting conditions to improve school environments.

Attention, memory and concentration

Blue-enriched light seems to improve attention and decrease the number of errors of shift workers14. Bright, blue-enriched light can also be used to sustain working memory among students during the post-lunch hours15. It has been suggested that use of dynamic ambient lighting may increase productivity in the winter16.


Light therapy has been used as a part of depression treatment for many years and effectively treats both seasonal and non-seasonal depressive symptoms. Published studies also show that a combination of pharmacological therapy and light is more effective than psychopharma alone, and chronobiological therapy is advancing17. Similarly, daylight exposure has been used to reduce depression symptoms in individuals with dementia, a group that is largely affected by depression18.


Learn more


  1. O’Hara-Wright M, Gonzalez-Cordero A. Retinal organoids: a window into human retinal development. Development. 2020 Dec 24;147(24):dev189746. 
  2. Wahl S, Engelhardt M, Schaupp P, Lappe C, Ivanov IV. The inner clock-Blue light sets the human rhythm. J Biophotonics. 2019 Dec;12(12):e201900102. 
  3. De Moraes CG. Anatomy of the visual pathways. J Glaucoma. 2013 Jun-Jul;22 Suppl 5:S2-7. 
  4. Mayo Clinic (2021) https://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/symptoms-causes/syc-20364651, accessed on 2022-01-20 
  5. Nagarajan V, Fonarow GC, Ju C, Pencina M, Laskey WK, Maddox TM, Hernandez A, Bhatt DL. Seasonal and circadian variations of acute myocardial infarction: Findings from the Get With The Guidelines-Coronary Artery Disease (GWTG-CAD) program. Am Heart J. 2017 Jul;189:85-93. 
  6. Figueiro, M. G. et al. The impact of daytime light exposures on sleep and mood in office workers. Sleep Health 3, 204-215, doi:10.1016/j.sleh.2017.03.005 (2017). 
  7. van Maanen, A. M. Meijer, K. B. van der Heijden, F. J. Oort, The effects of light therapy on sleep problems: A systematic review and meta-analysis. Sleep Med Rev 29, 52-62 (2016).​
  8. K. Grant et al., Daytime Exposure to Short Wavelength-Enriched Light Improves Cognitive Performance in Sleep-Restricted College-Aged Adults. Front Neurol 12, 624217 (2021).
  9. R. Knaier et , Dose-response relationship between light exposure and cycling performance. Scand J Med Sci Sports 26, 794-801 (2016).
  10. Rüger, M et al. Human phase response curve to a single 6.5h pulse of short-wavelength light. J Physiol (2013). 
  11. Münch, et al.Blue-Enriched Morning Light as a Countermeasure to Light at the Wrong Time: Effects on Cognition , Sleepiness , Sleep , and Circadian Phase. Neuropsychobiology274, 207–218 (2016).
  12. Musiek ES, Holtzman DM. Mechanisms linking circadian clocks, sleep, and neurodegeneration. Science. 2016 Nov 25;354(6315):1004-1008. 
  13. Gabel, V. et al. Effects of Artificial Dawn and Morning Blue Light on Daytime Cognitive Performance, Well-being, Cortisol and Melatonin Levels. Chronobiol. Int. 30, 988–997 (2013).
  14. Song et al., The Effect of Blue-enriched White Light on Cognitive Performances and Sleepiness of Simulated Shift Workers: A Randomized Controlled Trial. J Occup Environ Med 63, 752-759 (2021).
  15. Y. Zhou et al., Does Bright Light Counteract the Post-lunch Dip in Subjective States and Cognitive Performance Among Undergraduate Students? Frontiers in Public Health 9,  (2021).
  16. M. D. Canazei, P.; Staggl, S.; Pohl, W., Effects of dynamic ambient lighting on female permanent morning shift workers. Lighting Res. Technol. 46, 140-156 (2014).
  17. A. Geoffroy, C. M. Schroder, E. Reynaud, P. Bourgin, Efficacy of light therapy versus antidepressant drugs, and of the combination versus monotherapy, in major depressive episodes: A systematic review and meta-analysis. Sleep Med Rev 48, 101213 (2019). 
  18. Konis K, Mack WJ, Schneider EL. Pilot study to examine the effects of indoor daylight exposure on depression and other neuropsychiatric symptoms in people living with dementia in long-term care communities. 2018:1071-1077.