The effects of light on our sleep
How Light Affects Your Body, Sleep & Mood
Light is more than just something we see — it has a powerful effect on how our bodies function, how well we sleep, and even how we feel emotionally.
Our bodies run on an internal 24-hour clock called the circadian rhythm, which is controlled by a part of the brain called the suprachiasmatic nucleus (SCN). This internal clock is largely set by light. When light enters our eyes, it travels along specific pathways to the brain, signalling whether it's day or night and helping regulate everything from sleep to hormone production.
Light and Your Eyes
The eye contains different types of light-sensitive cells — cones, rods, and a special type called intrinsically photosensitive retinal ganglion cells (ipRGCs). These ipRGCs are particularly important because they're the main drivers of our non-visual responses to light, like controlling melatonin (our sleep hormone) and keeping our body clock on track.
Natural vs. Artificial Light
Outdoor daylight can reach up to 100,000 lux in direct sun, while a typical office is only around 500 lux. Our bodies evolved under natural sunlight, but today we're exposed to artificial light — LEDs, fluorescents, screens — around the clock. While these all look "white" to us, their light spectrums are very different, and those differences matter to our biology even if our eyes can't tell them apart.
Light and Sleep
Light is the strongest signal our body uses to time sleep and wakefulness. Getting bright natural light during the day has been shown to improve sleep quality, help you fall asleep faster, and even increase total sleep time. On the flip side, exposure to artificial light — especially blue-rich light from screens — in the evening can delay your body clock, suppress melatonin, and make it harder to fall asleep. Even reading on a tablet for a couple of hours before bed has been shown to push back sleep onset and reduce next-morning alertness.
Screens and Sleep
Smartphones and screens are a big part of the problem. The blue light they emit is particularly stimulating to the circadian system. While "night shift" or warm-tone screen modes can reduce some of this effect, they don't eliminate it entirely. The engaging nature of screen content also plays a role in keeping us awake longer.
Light and Mood
Light doesn't just affect sleep — it directly influences mood. It does this by regulating neurotransmitters like serotonin and by keeping our circadian rhythms stable. When our internal clock falls out of sync with the natural day-night cycle, it can contribute to mood disorders. This is why light therapy has become a recognised treatment for conditions like Seasonal Affective Disorder (SAD), non-seasonal depression, and even some anxiety-related conditions.
Light Therapy
Bright light therapy (BLT) involves sitting near a specialised lamp (typically 7,000–10,000 lux) for 30–60 minutes, ideally in the morning. It's most effective when done consistently and at the right time of day. It's been shown to work as well as antidepressants for some people, with minimal side effects. It's also being explored as a helpful tool for shift workers, people with jet lag, ADHD, borderline personality disorder, and even dementia.