How does light exposure affect memory?

Our bodies are tuned to the cycle of the sun. We evolved to experience sunlight during the day and darkness during the night. All of our major organ systems are affected by this daily rhythm, called the circadian rhythm. When our bodies experience patterns of light exposure different from the expected cycle, physiological processes get disrupted, leading to a variety of negative health outcomes [1].

Our daily rhythms are influenced by both the amount and the color of light we receive. White light, like the light we get from the sun, is a mixture of all the different colors. But the mixture varies throughout the day, containing more blue light in the morning and more red light in the evening. Bright white LED light bulbs contain a similar blue-rich color profile to the morning and mid-day sunlight, while soft white, or yellowish-looking incandescent light bulbs better resemble the red-rich color profile of the evening sunlight. Special cells in our eyes help tune our internal rhythms to the pattern of light and darkness we experience. These cells are especially sensitive to blue light, such that they promote wakefulness in response to blue-rich morning sunlight and restfulness when blue light levels decline.

The mechanisms that promote learning and memory are influenced by this cycle. Our brains are primed to learn new information during the day when there is a lot of light, and then to store it in long-term memory during the dark night as we sleep. Student performance increases when classrooms are illuminated with bright (blue-rich) lights [2]. Bright light exposure activates regions of the brain that promote alertness, and improves cognitive performance [3]. Light activates factors that are essential for memory formation [4], as well as factors that are important for the regulation of mood and overall brain health [1]. Studies have shown that when animals are exposed to constant dim light, instead of the natural cycle of bright light and darkness, they show impairments in learning and memory, as well as decreased levels of brain protective factors [5].

Unfortunately, many of us have become like the study animals exposed to constant dim light, instead of the natural cycle. Today, 99% of people in the USA experience some form of light pollution, or exposure to unnaturally high levels of light during the evening, from both indoor and outdoor sources [1]. As we spend more time indoors under dim artificial lights, we are also experiencing less of the high-intensity bright sunlight. For reference, sunlight is on the order of 10,000 lux, with lux being a measure of light intensity, while the full moon is on the order of 0.1 lux [1; 6]. The levels inside buildings tends to range from 100 to 1000 lux, with older incandescent lighting systems being considerably dimmer than newer LED-based lighting. Levels of evening outdoor light in residential areas is around 10 lux. This means we are getting at least 1000 times less light during the day and at least 100 times too much light at night. Additionally, the color distribution of most artificial lights is constant.

Mistimed light exposure disrupts hormone production, and can lead to an elevated stress response and mood disorders [7]. Evening light suppresses the production of the sleep promoting hormone melatonin, leading to insomnia and other sleep disorders. Individuals with dementia are particularly affected by disruptions to the circadian rhythm, which can exacerbate depression and agitation.

WHAT YOU CAN DO

There are efforts underway to better design our living spaces with lighting that is more in tune with our biology [8]. Until some of these practices become widespread, we may not have much control over light pollution stemming from the outdoor environment. However, we can make changes to our daily routine and exposure to indoor light. Pilot studies have found that the implementation of these strategies, namely bright light therapy in the morning and reduced light exposure during the evenings, improved sleep consolidation and mood, while reducing agitation in patients with dementia [9; 10].

1. Get more bright blue-rich light during the morning

• Go outside. The best thing you can do is to go sit or take a walk outside in the direct sunlight during the morning hours, ideally between the hours of 8 and 10 AM for about 30 minutes.
• Be near a window. When going outside is not possible, some of the benefits of sunlight exposure can be obtained by sitting near a window. However, you need to sit within 3 meters of the window to receive a sufficient level of sunlight [1].
• Keep lights bright and blue-rich. Full spectrum bright white/blue lights can also be used to illuminate indoor spaces during morning hours. These can be used as a part of light fixtures, though the placement of the lights needs to be taken into consideration in order to avoid uncomfortable glare.
• Use a light box. Light can be applied to the face in a more targeted manner without the risk of UV damage through the use of a light box for a set period of time during the morning hours.

2. Minimize light exposure, especially blue light, during the evening

• Keep lights dim and red-rich. Indoor lights should be dim, such as soft or warm white bulbs, during evening hours. Smart, dynamic lighting systems are being developed that automatically adjust the intensity and color spectrum of the light, so it is brighter and bluer during the day, and dimmer and redder during the evening [9].
• Use blue-blocking filters. Electronics are a major source of blue light, and many phones and computers have settings to apply filters during evening hours to block the blue light. Blue-light filtering glasses can also be used.
• Sleep in darkness. Blackout curtains and eye masks during sleep can minimize the effects of environmental light pollution.
• Use nightlights strategically. Nightlights are often used in children and the elderly to prevent falls, but research shows that lights can be better targeted to promote navigation while reducing the negative effects of nighttime light exposure. This includes the use of LED light panels outlining doorways, pathways of light on the floor that guide to the bathroom, and motion-activated lights [11].

Adopting these practices to reset our rhythms back in tune with the natural sun cycle can improve our overall health and sense of well-being throughout life.

1. Bedrosian TA, Nelson RJ (2017) Timing of light exposure affects mood and brain circuits. Transl Psychiatry 7, e1017-e1017.
2. Choi K, Suk H-J (2016) Dynamic lighting system for the learning environment: performance of elementary students. Opt Express 24, A907-A916.
3. Vandewalle G, Balteau E, Phillips C et al. (2006) Daytime Light Exposure Dynamically Enhances Brain Responses. Current Biology 16, 1616-1621.
4. Inami S, Sato S, Kondo S et al. (2020) Environmental Light Is Required for Maintenance of Long-Term Memory in Drosophila. The Journal of Neuroscience 40, 1427-1439.
5. Soler JE, Robison AJ, Núñez AA et al. (2018) Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus). Hippocampus 28, 189-200.
6. NOAO Recommended light levels.
7. Smolensky MH, Sackett-Lundeen LL, Portaluppi F (2015) Nocturnal light pollution and underexposure to daytime sunlight: Complementary mechanisms of circadian disruption and related diseases. Chronobiology International 32, 1029-1048.
8. Zielinska-Dabkowska KM, Xavia K (2018) An Overview of the Cognitive and Biological Effects of City Nighttime Illumination Including a London Case Study. London: Conscious Cities Anthology 2018: Human-Centred Design, Science, and Technology.
9. van Lieshout-van Dal E, Snaphaan L, Bongers I (2019) Biodynamic lighting effects on the sleep pattern of people with dementia. Building and Environment 150, 245-253.
10. Figueiro MG, Plitnick BA, Lok A et al. (2014) Tailored lighting intervention improves measures of sleep, depression, and agitation in persons with Alzheimer's disease and related dementia living in long-term care facilities. Clin Interv Aging 9, 1527-1537.
11. Hanford N, Figueiro M (2013) Light therapy and Alzheimer's disease and related dementia: past, present, and future. J Alzheimers Dis 33, 913-922.

Get the latest brain health news:

Subscribe