Motivation and emotion/Book/2025/Lighting and mood

Imagine this... Meet Sigurd, a resident of Tromsø, Norway, who experiences this polar night each year. As the daylight fades to almost nothing, Sigurd notices his energy draining, his mood sinking, and his nights stretching longer with restless sleep. He feels sluggish and disconnected, struggling to find motivation in daily tasks. Throughout this time, the lack of natural light disrupts his internal biological clock, making it difficult to maintain a regular sleep schedule and regulate his emotions.

Light is a fundamental element of our environment, helping us to shape not only how we see the world, but also how we feel, think, and behave, both at conscious and unconscious levels. Beyond just enabling us to see, light can influence our biological processes, emotional regulation, and cognitive performance (Vandewalle et al., 2009; Wurtman, 1975).

Lighting conditions unsuited to their environment, whether in the home, workplace, school or in public spaces, can disrupt biological and psychological processes that drive mood regulation (Bedrosian & Nelson, 2017). For instance, research has demonstrated that insufficient daylight exposure can lead to depressive disorders, such as Seasonal Affective Disorder (SAD) (Partonen & Lönnqvist, 1998; Rosenthal, 1984), while excessive or poorly calibrated artificial lighting has been linked with heightened stress, reduced concentration, and visual discomfort (Begemann et al., 1997; Knez, 1995).

Given that many people living in industrialised societies spend the majority of their time indoors (Klepeis et al., 2001), the quality and characteristics of artificial lighting have become a determinant of psychological well-being and both long and short term mental health (Lunn et al., 2017). In this chapter, we will delve into the complex interplay of environmental, biological and psychological factors that underpin the relationship between mood and lighting.

Mood is a sustained, affective state that shapes an individual’s perception, cognition, and behaviour over extended periods of time (Clark et al., 2018; Sekhon & Gupta, 2023). Unlike brief and intense emotions, such as fear or joy, moods are enduring and are less directly tied to specific stimuli (Beedie et al., 2005). Moods can vary along a spectrum ranging from positive states, such as happiness and contentment, to more negative states such as sadness and irritability. Research demonstrates moods are the result of both internal biological fluctuations such as hormonal and neurotransmitter changes and external environmental influences (Rautio et al., 2017; Wirz-Justice, 2006).

Mood regulation is influenced by multiple neurotransmitters and hormones, such as serotonin, dopamine and norepinephrine (Jiang et al., 2022; Liu et al., 2018), and imbalances in these systems are often linked to depression and anxiety disorders. Along with these major neuromodulators, several key brain structures are implicated in the shaping of moods, namely the amygdala, prefrontal cortex (PFC) and thalamus. These all aid in the integration of sensory information relevant to a person's mental and emotional state (Drevets, 2006).

Light plays an important role in regulating mood through its effects on both circadian rhythms and the body's hormonal systems. The body’s internal clock relies on external cues to align certain processes, including telling our body when to be alert.

The suprachiasmatic nucleus (SCN) in the hypothalamus (see Figure 3), receives light information and coordinates timing signals to peripheral clocks throughout the body which tell the body when to be alert or when to be at rest (Weaver, 1998). This light information is detected by intrinsically photosensitive retinal ganglion cells (ipRGCs), and are especially sensitive to blue light (Do & Yau, 2010). These cells send signals directly to the SCN through the retinohypothalamic tract, operating independently of vision and responding to overall brightness. After receiving this information, the SCN then controls the release or suppression of melatonin and cortisol, which modulates the body's sleep-wake cycle and alertness in accordance with the amount of available light (Castaño et al., 2019).

The impact of light on circadian rhythms varies depending on its source, with natural and artificial light each affecting the body in different ways. Sunlight changes brightness throughout the day, helping to regulate and synchronise circadian rhythm by providing cues.

As light is the primary cue for synchronising circadian rhythms, regular exposure to daylight helps to stabilise the internal body clock, whereas irregular or poorly timed artificial lighting (such as the prolonged use of screens at night) suppresses melatonin and disrupts these circadian rhythms (Green et al., 2017, Tähkämö et al., 2018). Morning daylight exposure is linked to improved mood and more stable sleep-wake patterns, and has proved a key treatment component for seasonal disorders (Figueiro et al., 2017).

Natural light has a broad spectral range, including ultraviolet radiation, and temporal variations, which can have biological effects not accounted for in current standards for artificial lights (Thorington, 1985). Higher illuminance levels are associated with improved alertness and cognitive performance. Exposure to bright light during the day can increase mood and reduce drowsiness. (Campbell & Dawson, 1990; Smolders et al., 2012).

Imagine this... Despite it being a school night, Sarah decides to finish the new season of the show she has been waiting for. After a disappointingly anti-climactic finale, she looks up to find the clock is reading well into the early hours of the morning. Resigned to her fate, she sets her alarm to go off in a few hours, and lays back down. Despite her obvious signs of fatigue, the short-wavelength blue light emitted from the screen has confused her brain, and she will still be awake and unable to sleep when the morning sun begins to glare through her bedroom curtains...

Artificial lighting, such as that from screens/LEDS or fluorescents, halogens, neon lighting, HID lights) can either mimic these natural light patterns or disrupt them, which influence sleep quality and subsequently, mood (LeGates et al., 2014).

Differing wavelengths can influence hormone secretion/brain activity, with the short-wavelength blue light (470 nm) having been found to suppress melatonin secretion, and promote wakefulness and concentration (Chellappa et al., 2011). Long-wavelength red light (650 nm) has been evidenced to promote the release of melatonin (Milone et al., 2015), and can encourage relaxation and calmness (Chen et al., 2024; Ham et al., 2022).

Light exposure at night, common in many environments such as offices or hospitals, is linked to disrupted circadian rhythm, impaired emotional regulation and heightened stress responses (Cajochen et al., 2011; Tähkämö et al., 2018).

Prolonged exposure to environments with irregular light has been linked to mood disorders and cognitive deficits (Bedrosian & Nelson, 2017; Bedrosian & Nelson, 2013).

Controlled exposure to specific lighting conditions have been applied to improve both general wellbeing and in the treatment of specific mood and sleep disorders, applying the biological effects of light on circadian rhythms, hormone release and alertness.

One of the most established applications is bright light therapy, which involves daily exposure to intense artificial light (around 10,000 lux) for up to 20 to 30 minutes a day (Kogan & Guilford, 1998). Bright light therapy has been shown to be particularly effective in the treatment of Seasonal Affective Disorder (SAD), where it helps decrease depressive symptoms brought on by the reduced daylight in winter months (Pail et al., 2011). Research also suggests it may have benefits outside the treatment of SAD, with several studies indicating improved sleep, energy and overall mood (Pail et al., 2011; Wirz-Justice, 2006).

The therapeutic potential of light-based treatments has also been investigated within the context of clinical environments. Optimised hospital lighting can reduce stress and support patient recovery (Dalke et al., 2006), and blue-enriched light can increase alertness in night-shift workers (Campbell & Dawson, 1990, Chellappa et al., 2011; Smolders et al., 2012). However, findings remain uncertain, with studies on dynamic lighting systems designed to mimic natural light patterns have shown results in increasing circadian health (Zhang et al., 2020), whilst other studies reported no significant effects on staff wellbeing (Simons et al., 2018).

New research is currently exploring the potential benefits of personalised or adaptive light systems in workplaces and schools, which allow for adjustments in intensity and colour temperature in an effort to support alertness, focus and mood throughout the day (Barkmann et al., 2012). Light therapy has also shown promise in cognitive improvement for those with ADHD, and as a potential alternative to medication for antepartum depression (Terman, 2007).

Light is more than simply a means of vision, it is an important regulator of human biology, cognition, and emotion. Through its influence on circadian rhythms, hormonal systems and neural processes, lighting conditions help shape and contribute to the determination of mood, alertness and long-term mental health. Research demonstrates that whilst natural daylight supports healthy circadian rhythms and wellbeing, poorly timed or inappropriate artificial light can disrupt sleep and contribute to stress, cognitive impairment and mood disorders. Clinical applications, such as bright light therapy, help showcase the therapeutic potential of harnessing light exposure, and innovations into adaptive lighting suggest promising avenues for the enhancement of psychological health in everyday urban environments. Further research into the interaction between light and mood may help inform not only medical interventions, but the design of homes, workplaces, and public spaces that can better support societal wellbeing.

• Circadian rhythm (Wikipedia)
• Lighting (Wikipedia)
• Melatonin and circadian motivation (Book chapter, 2025)
• Mood (Wikipedia)
• Omega-3 fatty acids and mood (Book chapter, 2020)

• Blue light has a dark side (Harvard Health Publishing)
• How does lighting affect mental health in the workplace? (Forbes)
• How smartphone light affects your brain and body (Business Insider)
• How does the human eye work? (BBC)