8.4 Exposure to Light Impacts Sleep

Circadian rhythm is mostly guided by light and darkness, which means people tend to feel most tired between midnight and 7 a.m. Some strategies for optimizing this natural cue for sleep are to:

• wake up with the sun, if possible, by keeping blinds or curtains open;
• turn on bright lights to help your body get going when you wake up; and
• get natural sunlight for at least 30 minutes each day, whether that means being outside or sitting near a window, when possible.

Melatonin is influenced by exposure to any kind of light: sunlight and artificial light. If you want or need to sleep, avoid bright natural light and screen time, such as watching TV or using a computer, tablet, or smartphone right before bed; light can trick the internal clock into thinking it’s time to remain awake, making it hard to fall asleep. Some research suggests that while individuals’ preferences or natural sleep tendencies may lead to later bedtimes or wake up times, these preferences or natural rhythms might be amplified by exposure to light, like light from devices (Phillips et al., 2017). Research appears to show that if light-emitting devices were eliminated, differences in circadian timing among individuals would likely not exist to the same extent (Wright et al., 2013). In other words, we would all have the same circadian timing if we were exposed to the same amounts and types of light.

For better sleep, avoiding use of light-emitting electronics before sleep is recommended, but if you must, dim the brightness of the device or use settings or features that filter out short-wavelength or blue light as bedtime approaches. Blue or short-wavelength light is shown to impact melatonin levels more strongly than other wavelengths (Chellappa et al., 2011).