Light Pollution: Too Bright at NightIn the News
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- Apr 20
- 4 min read
When we think of pollution, we tend to think of toxic chemicals in our environment. We don’t tend to think about pollution from a good thing, such as light, but just at the wrong time and place.
Historically our night times were dark, lit only by the moon, and the occasional shooting star or maybe the aurora borealis, depending where we lived. Any light we used after dark was from a fire or a candle, both of which provide a yellow-golden light. This colour was emulated by incandescent light bulbs. In contrast our daytimes were bright, under blue skies.
Now that we have lights that make things as bright as day, we can work into and through the night. And that light is often blue light, more like daylight. That light may be provided by LED bulbs that have replaced the softer light of incandescent bulbs. Plus we often spend time looking at screens, which emit blue light.
Over the past few years research has linked nighttime light exposure to a broad range of health concerns: far more than just the obvious weariness from disruption in the quantity and quality of our sleep. Throwing off our internal clocks produces a cascade of effects across various systems, taking a toll on nearly every aspect of our health. It has been shown to have negative effects on cardiovascular, metabolic, cognitive, and mental health, hormonal balance, organ function, and inflammation levels. It is linked to higher risks of ailments from obesity and diabetes, to accelerated brain aging and cancer (resulting in earlier mortality). In short, we have found that our circadian rhythms are closely linked to our overall health.
Light is the most important time cue for the body clock. It has acute effects, such as the ability to shift melatonin, spike cortisol, and even alter our reproductive hormones. The latter is probably why women used to refer to their periods as their “moon time” because when left undisrupted by additional light sources, women’s periods often aligned with the cycles of the moon.
Cardiovascular health effects: A cohort study of nearly 89,000 adults over 40 years old, over a period of 9.5 years, was published in JAMA in October 2025. It found that exposure to lights after sundown increased cardiovascular risk by up to 50%. Brighter light at night was associated with higher risks of coronary artery disease, heart attacks, heart failure, atrial fibrillation, and stroke. And this was independent of established cardiovascular risk factors.
Blood sugar regulation and metabolic health: People who slept in a room with light experienced increased activation of their sympathetic nervous system — the “fight-or-flight” response — and had elevated heart rates during the night. The light exposure the night before negatively impacted their blood sugar regulation, resulting in higher glucose levels the next morning.
Cancer risk: Studies have associated persistent circadian disruption, such as that experienced by frequent night shift workers, to an increased cancer risk.
Colorectal cancer is linked to light at night, as is breast cancer in women, and prostate cancer in men.
Mental health effects: Circadian rhythm disturbance is known to be a common feature of many psychiatric disorders. A large study published in Nature Mental Health in November 2023 studied the effects of greater nighttime light exposure in 86,772 older adults. It found that those with greater exposure had significantly higher risks for major depressive disorder, generalized anxiety disorder, post-traumatic stress disorder, psychosis, bipolar disorder, and self-harm behaviour, compared with those who had darker nights. Nighttime light exposure has also been tied to hyperactivity, abnormal social behaviour, and learning and memory deficits.
Conversely, greater daytime light exposure is associated with less risk for major depressive disorder, PTSD, psychosis and self-harm behaviour.
That study states: “Avoiding light at night and seeking light during the day may be a simple and effective, non-pharmacological means of broadly improving mental health.”
How can you create a healthy light and dark rhythm in your life?
Use soft lights after dark. If you’re exposed to a lot of bright light just before bedtime, your brain just thinks the day hasn’t ended yet.
Avoid screens for as long as you can before bed.
Avoid lights in the bedroom other than your reading light. If you have to get up in the night, turn on as little light as possible, because the brighter the light, the more effect it has on melatonin* production. Try using a gentle light near the floor, preferably with a motion detector so that it only turns on when you are up.
Where you can, avoid LED lights as they can be especially disruptive to circadian rhythms.
Use an alarm clock that doesn’t have a lighted display.
If you have fire or carbon monoxide alarms with lights, position them just outside the bedroom, rather than on the bedroom ceiling.
Keep electronics with flashing lights out of the bedroom, especially your router, to reduce both light and wi-fi exposure.
Get black-out blinds or curtains.
Use a soft light before dawn. A 4 or 7 watt plug-in, non-LED or opaque night-light will give enough light to make your morning tea or coffee, while still allowing for a more gentle wake-up.
As early after daybreak as you can, get outside for at least half an hour. Getting exposed to the full spectrum of daylight starts synchronizing your circadian clock.
Get healthy blue light exposure during the day. Move your desk near a window or take breaks outside.
Get back to your natural rhythm as much as possible: soak up natural blue light during the day and block man-made blue light in the evening.
We know that people, animals and plants need their light and dark cycles. This does not appear to have been properly taken into account in proposals to use satellites with mirrors to reflect light onto dark areas of the earth. A guardian newspaper article has more information on that topic:
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