I once travelled to the Arctic Circle in February and experienced life with minimal natural light.

I was with a group of professional musicians, playing in the exquisite ‘Ice Cathedral’ in Tromso. There is so much that I could say about this beautiful experience, but for this post, I am focusing on light. The light in Tromso was hazy at best, and reality felt dreamlike, when we were outdoors. Indoors, of course, artificial lighting made everything feel completely normal.

On another trip, this time to Helsinki, again in February, the darkness, like the snow, felt very permanent. There was fleeting sense of light but it disappeared as soon as I'd registered it. I was attending a meeting to discuss Masterclasses in Conservatoires. Much to our surprise, our fabulous hosts offered coffee, chocolate cake and red wine every two hours to help maintain our serotonin levels. The long winters take their toll on health and well-being in the northern latitudes, and this was one way to keep our levels healthy.

How light regulates the brain’s internal clock

Light doesn’t only help us see. It tells our body when to wake, rest and repair.

Researchers agree that our bodies can almost tell the time, using our natural responses to light (Lee et al, 2020). Changes in light intensity are detected by photosensitive rods and cones in the retina of the eye. They contain the photopigment melanopsin which is sensitive to short-wave light. These cells send signals to the master circadian clock of the superchiasmic nucleus (SCN) in the hypothalamus. This information’s relayed to the other circadian clocks in the brain and impact the endocrine system and serotonergic tone, as well as states of alertness. Those who study seasonality of moods and seasonal affective disorder find serotonin production is related to the hours of sunlight (Schollhorn et al 2023). Of course mood is not only influenced by light, but also by many other factors such as alertness, attention and anxiety, in addition to neurotransmitters such as dopamine, serotonin and noradrenaline (Stewart and Albrecht, 2025).

Isn’t it remarkable how our bodies are so finely entrained to the light-dark cycles of day and night and seasonality?

Here in London, (UK) we do feel the seasonal changes in light, even though we are so far south, when compared with Helsinki and Tromso. So, what is really happening? There are three real changes.

1. Reduced hours of sunlight,

2. Lower light intensity, even at midday,

3. A lower proportion of short-wave (blue) light.

The reduction in short-wave blue light is key because this is what we need to keep our internal circadian clock synchronized with the light and dark cycle of our external environment and also to prime the complex clock system of our internal biology. The optimal functioning of our cells and organs is orchestrated by the central clock in our hypothalamus, which is primed by the light sensitivity retinal cells of our eyes.

Why alertness has a rhythm - and winter flattens it

The rhythm of alertness is entrained to the sky

Norwegian researchers (Bjerrum et al., 2025) described alertness as following a circadian rhythm. It begins low in the early morning, but builds during the day and drops off again in the evening and at night. They described how alertness could be increased, and drowsiness could be decreased by using short-wave enriched white light and investigated the effects of light on attention levels in students. Light improved attention and alertness, but there was no statistically significant difference between the effect of short-wave or long-wave light. Swedish researchers studied office workers and found that alertness in wintertime was related to whether they had had a 30 minute exposure to light during their lunch break. The benefits were found to last for an hour after returning to the workplace (Adamsson et al., 2018).

These studies point to the importance of getting outdoors every day and making the most of midwinter light, but the more nuanced data suggest that the change of light quality in the afternoon is salient. For example, retinal cells were sensitive to short-wave blue light in the morning but not in the late afternoon. This is why we benefit from early morning light exposure. Our circadian system has evolved to detect particular light qualities in the morning, but not later in the day. In other words, our circadian amplitude and our 'wave' of alertness may ‘flatten’ in the winter because we are exposed to less light, but it retains its essential rhythm.

The cognitive purpose of winter: Rest, repair and recuperation

If our alertness feels flat and the motivation to be productive has dropped off, this is what nature intended. It’s the rhythm of rest and repair The lower light signals scarcity of food and a season of replenishment rather than one of plenty. We are learning that fasting is a natural state in which our bodies run maintenance and repair programmes as we sleep. In our culture, there’s an expectation that productivity remains the same all year round and that we over-ride the natural rhythms of rest and repair. There’s a sense of safety in routines and familiar patterns because these conserve energy and ensure time for rest.

Artificial light, modern life and circadian disruption

In terms of data there is little evidence that we are influenced by seasonal light changes because exposure to artificial light protects us from this. Dunster et al (2022) showed that exposure to artificial light in the autumn and winder months affects the sleep wake cycle, with students delaying their sleep and waking up later in the morning. They also showed that exposure to daylight can prevent this level of circadian disruption. This is important because circadian disruption is not only a matter of a shift in the body clock, but a change to the delicate balance to the synchrony of the organs of the body (most have their own clock system) and the clocks that govern individual cells of the body.

What the rhythm of rest means for schools and classrooms

Thinking about the quietness, the darkness and the scarcity of food at this time of year, it makes sense that this was a time for rest, recuperation and retreat. Our 24/7 culture tends to encourage non-stop effort and this is possible for a while, but is not sustainable. So rather than heading at full speed towards depletion, think about rhythmic poise and introduce a reflective moment.

In the classroom, this might translate into consolidation and celebrating all the effort and steps that have been taken during the year. How many categories might there be? Many schools recognize endeavour in many different domains, such as academics, sports, music and drama. But as well as the obvious accomplishments, it’s very important to celebrate moments of kindness, moments of hilarity and of course bravery.

Honoring rhythm: From seasonal rest to renewed learning

Just as the light returns after winter, so too can our energy and creativity when we honor the rhythm of rest. If you’d like to explore how rhythm can support focus, flow and learning in the new term, details of January’s Rhythm for Reading CPD course are available here.

References

Adamsson, M., Laike, T., & Morita, T. (2018). Seasonal variation in bright daylight exposure, mood and behavior among a group of office workers in Sweden. Journal of Circadian Rhythms, 16(1), Article 2. DOI: 10.5334/jcr.153.

Bjerrum, L. B., et al. (2025). Light of both high and low melanopic illuminance improves alertness and influences circadian entrainment. Scientific Reports. DOI: 10.1038/s41598-025-29154-4.

Dunster, G. P., et al. (2023). Daytime light exposure is a strong predictor of seasonal variation in sleep and circadian timing of university students. Journal of Pineal Research. DOI: 10.1111/jpi.12843.

Lee, E. E., et al. (2020). Daily and seasonal variation in light exposure among the Amish and general population: physiological and behavioural implications. PMC Biology Reports.

Schönhorn, I. et al., (2025). Seasonal and daily variation in indoor light exposure and associations with disrupted sleep and physiological rhythms. medRxiv preprint. DOI: 10.1101/2024.10.30.24316428.

Stewart, D., & Albrecht, U. (2025). Beyond vision: effects of light on the circadian clock and mood-related behaviours. npj Biological Timing and Sleep, 2(1), Article 12. DOI: 10.1038/s44323-025-00029-1.