light and the body
Excerpt from The Life Machines:
The light-detecting cells in our eyes that notify the SCN that there’s light outside are particularly good at detecting blue light, the light they get from the sun. This is perfect in the morning, but blue light in the evening sends our body the wrong message. What does it mean in terms of getting a good night’s sleep here on Earth? Sleep experts point out four things:
Being exposed to sunlight first thing in the morning will send your SCN a two-word message: Good morning! Because you spent the previous few hours in darkness, your system is more sensitive to light in the morning, so even a relatively small amount of light can be effective. (Remember, never look directly at the sun because it can permanently damage your retina.)
Spending time outside during the daytime helps, too. This is true even if it’s cloudy. You’re getting much more light outdoors than indoors.1 Being outside makes the master clock more robust and helps it synchronize not only with the outside day, but also with peripheral clocks in your body.
Be mindful of blue light–emitting screens. Some experts recommend avoiding screens at least an hour before your usual bedtime. It seems that the effect of TV screens at a distance is not as detrimental to your sleep as screens that are close to your face. If you were exposed to a lot of natural light outside during the day, you may be less affected by the light from the screens. Kids are more sensitive to light, so they are more likely to be affected.2
Many experts agree that you should sleep in a cool and totally dark room and not turn on the light if you wake up in the middle of the night, especially not any equipment that emits blue light, like your phone or tablet. While the evidence for this recommendation is strongest for children, the body of evidence continues to evolve for other age groups. “The influence of light never ceases to amaze me in that every year it seems we learn something new about how powerful light is and how [even] little light exposure is impactful,” Flynn-Evans says.
———————
1. “Screen Time and Sleep—It’s Different for Adults | Restorative Sleep,” Lifestyle Medicine (blog), August 8, 2024, https://longevity.stanford.edu/lifestyle/2024/08/08/screen-time-and-sleep-its-different-for-adults/.
2. Lauren E. Hartstein et al., “The Impact of Screen Use on Sleep Health across the Lifespan: A National Sleep Foundation Consensus Statement,” Sleep Health 10, no. 4 (August 2024): 373–84, https://doi.org/10.1016/j.sleh.2024.05.001.)