Light · Protocol 3 of 5
Keep your last hours dim and warm
1In 30 seconds
In the hour before bed, use only as much light as you need to move around safely, and keep it dim, low and warm. Bright white LEDs and screens raise cortisol and cut melatonin, which harms sleep, mood and metabolism. If you cannot control the lights, glasses that block short wavelengths can help.
2Picture it
3Why do it
- 1
Dim, warm light at night lets melatonin rise and keeps cortisol low, so you fall asleep more easily and wake less in the night.
- 2
A study of nearly 87,000 people linked darker nights with lower risk of depression, anxiety and self-harm, whatever their daytime light.
- 3
Even a dim 100 lux ceiling light left on while you sleep can upset your blood sugar the next morning.
4How to do it
- Plan your day in phases: bright light 0 to 1 hour after waking, some sun 6 to 10 hours after waking, and dimming from 10 to 14 hours after waking.
- In the final hour before bed and until morning, switch off ceiling lights and use only lamps placed low, such as a table or floor lamp.
- Choose warm yellow-amber bulbs, or red bulbs, for your evening rooms, since they give off few short wavelengths.
- Put your phone away, or turn its brightness right down, during this last hour.
- When you cannot control the lighting, as in hotels or on night journeys, wear glasses that block all short wavelength light, not just basic blue blockers.
- Do not worry about moonlight or candlelight, which are too weak to wake your brain; a full moon gives less than 1 lux.
5Make it work in India
- Many Indian homes use bright white tube lights and ceiling LEDs. After dinner, switch to one warm table lamp or a low-wattage yellow bulb in the main room.
- In a joint family where others watch TV late, sit further from the screen, keep the room lights low or wear short-wavelength blocking glasses.
- For night-shift workers, your night is the morning. Wear sunglasses on the way home, and use blackout curtains or a thick dupatta over the window while you sleep.
6The long read: the science2 min read · tap to open
Your body treats light very differently at the two ends of the day. In the morning, you need plenty of bright light to boost cortisol and wake up. At night, a small amount is enough. Light at night also squashes melatonin, so it makes you more alert and less sleepy at the same time.
The light-sensing cells that tell your brain ’it is daytime’ sit in the lower part of your retina, so they look upwards. Outside they see the sky. Indoors they see the ceiling. That is why ceiling lights are so disruptive at night, and low lamps are much gentler.
These same cells connect to more than your body clock. They link to sleep areas of the brain and to a small region nicknamed the ’disappointment centre’, which damps down dopamine, a feel-good brain chemical. Bright light at night can switch this area on, which may help explain why late screens can leave you feeling low.
Big studies point the same way. In one, almost 89,000 people in the UK wore light sensors for a week and were followed for about eight years. Those with the brightest nights had up to 34 per cent higher risk of dying from any cause than those with the darkest nights. Those with the brightest days had up to 34 per cent lower risk. Very bright light between 1 a.m. and 6 a.m. was tied to a 20 to 67 per cent higher risk of death from heart and metabolic disease. These are links rather than proof, but they are hard to ignore.
Strong evidence Many studies show that light at night cuts melatonin, and very large studies link brighter nights with poorer physical and mental health, though those links cannot prove cause.
Questions people ask
I fall asleep fine with the TV on. Does this matter for me?
It may still matter. Night light has been linked to higher blood pressure, weight gain, and poorer mood and thinking the next day, even when sleep seems fine.
Is my phone’s night mode enough?
It helps a little by warming the colour, but a bright screen close to your face is still a lot of light. Turning the brightness right down, or putting the phone away, works better.
Is a red bulb the same as red light therapy?
No. A dim red bulb at night is simply a gentle light that leaves melatonin alone. Red light therapy uses strong panels for a different purpose, covered in Protocol 5.
7Be careful
Keep enough light to move around safely, especially on stairs and for older family members at night. Never wear short-wavelength blocking glasses while driving, because they can make blue and green things, including traffic signals, hard to see.
8Try it for 7 days
Tap a day each time you dimmed lights before bed.
From the book: “Avoid Viewing Bright Light One Hour Before Your Bedtime” (Light Protocol 3). Evidence rating and India notes are our own.