Elizabeth Saenger, PhD
To figure out whether, and when, you need protective eyewear, you need to know about the kind of light that can disrupt your sleep, or harm your eyes. And you need to know that the kind of light you might see for up to three hours before you go to bed can keep you up at night.
In other words, getting ready for bed really means getting your eyes ready for bed about two to three hours before your head touches the pillow. Before the advent of candles, and electricity, such advanced planning was not necessary because Mother Nature turned off the light at sunset.
What kind of light disrupts sleep?
Blue light is part of the spectrum of white light, as the English genius Isaac Newton (1643-1727) discovered when he shone white light through a prism. As scientists discovered centuries later, it is this part of the spectrum that has special effects on our nervous system.
First, when blue light hits cells in the retina–cells not related to vision, but to regulating our circadian rhythms, or internal clock–it tells our bodies that it is daytime. This message energizes us, which is fine when we want to listen to a lecture, or play tennis, but not convenient if we are trying to relax.
Second, exposure to blue light in the evening, or during the night, tells our body that it is still time to be awake, and pushes our body’s perception of bed-time into the future. That’s why exposure to white light before going to bed is likely to keep you up.
For the same reason, exposure to night lights with white light make it harder to go back to sleep if you get up in the middle of the night.
Third, blue light at night can harm the eyes. At the risk of oversimplifying the mechanisms involved in sleep, the hormone melatonin, released daily by the pineal gland, is most abundant at night. Melatonin’s presence in the retina makes us more sensitive to blue light. Consequently, at night we are most attuned–and vulnerable–to blue light.
Amber glasses, like those here, allow you to work under bright white lights without a problem because the glasses filter out the right part of the spectrum. Consequently, these glasses can also help you get to sleep earlier if worn for the two to three hours before bedtime.