Humans evolved to be in the sun from sunrise to sunset and relative darkness once the sun went down. The pattern of light to which we are exposed to over a 24 hour period keeps our body's internal clock aligned with our external environment. The backs of our eyes contain special cells which are exquisitely sensitive to the blue-green light portion of the visible spectrum (because the intensity of blue-green light changes the most as the sun moves in the sky, with little blue light at sunrise/sunset, lots of blue light at noon). When our eyes detect blue light, they send a signal directly to a "master clock" deep within our brain which in turn releases hormones into our blood which circulate through the body to let it know the time of day. The stronger the intensity of blue-green light, the stronger the signal from our eyes to our brain and body. Additionally, exposure to bright blue light during day stimulates our brains and bodies to be maximally alert.
Before the existence of artificial lighting, we would have been exposed to intense blue light nearly continuously during the day (with some amount of variation depending on time of day, season, latitude), and virtually no blue light once the sun went down. In our modern society, however, many of us get only medium (or even low) intensity blue light during the day, and increasingly more blue light in the hours after the sun goes down from artificial lighting and screens (the light emitted from most backlit screens is actually enriched for blue light). This aberrant pattern of light exposure confuses our brain and internal clock, making the brain think that it is perhaps in a perpetual northern latitude summer, or, that sun sets and rises much later than it actually does. This can lead difficulty falling asleep, reduced sleep quality, difficulty waking up in the morning, daytime sleepiness, fatigue and a host of other problems. Even if a person does not report difficulty falling asleep or reduced sleep quality, close examination of their sleep during a formal sleep study may still reveal disruption from blue light.
Fortunately, by knowing about the biologic effects of blue light you can actually use it to your advantage to create a robust internal clock and improve your sleep and alertness (be sure to wear sun protection where appropriate, the brightness of sunlight is typically sufficient to stimulate the necessary pathways even WITH sunglasses on, in the shade, on a cloudy day). Try the following techniques.
To increase Blue/Bright light during the day:
- Open the window shades as soon as you wake up in the morning and/or turn on the lights to full brightness.
- Go outside or get exposure to even brighter light (such as from a 10,000 lux lightbox) starting around 30 minutes after waking, for at least 30-60 minutes. You can go for a walk outside, eat breakfast outside. Keep a warm coat, hat/gloves by the door to make this as easy as possible.
- Increase your level of blue light exposure during the day by working near a window or install blue-enriched, bright artificial lights (look for a product which mimics sunlight or you consider purchasing a “10,000 lux” lightbox and have it running until shortly before sunset).
- Add additional sunlight exposure during the day by eating lunch outside, holding 1:1 meetings outside and/or going for a brief walk around the block whenever possible.
To reduce Blue light in the evening: (blue light reduction should start at least 2 hours before your desired bedtime)
- Make sure room lights have an orange-red tint (such as an edison-style light bulb, “warm” color LED, or amber light bulb) and keep the room lighting as dim as you can comfortably tolerate. You can use an additional book light if needed, again ensure it has a warm tint bulb (“amber light”) rather than a white-blue tint bulb. There are several vendors who make “amber” or “blue free” reading lights and room lights, you can find them on amazon or through google. There are also increasing numbers of “smart lights” which can change from blue-white during the day to orange-reddish at night. Alternatively, you can also purchase special glasses (“blue blocking glasses”) to filter out the blue wavelengths of light (in research studies, blue blocking glasses are the MOST effective method of eliminating the effects of evening blue light).
- Redden and dim the screens of ALL devices used in the 2 hours before bed. Many electronic devices allow you to do this automatically: enable “NightShift” on your iPhone/Mac computer, “Night Light” on your PC, “Blue Shade” for Kindle Fire, “Blue light filter” for Samsung, try "cinema mode" on your TV settings, download "F.LUX" app or “Twilight” if your computer does not offer a red-tint in settings.
- Add a warm-tint night light to your bathroom and ideally get ready for bed with JUST THAT LIGHT. If you must use the full overhead lighting, do your bedtime routine at least 1-2 hours before you get into bed for the night.
- Make sure the bedroom is dark at night and not getting light from a streetlight, cars, or other outside sources. A red colored night light is ok to use if necessary for comfort or safety. Keep all screens out of the bedroom and do not look at them during the night.
Lastly, keeping the same bedtime and waketime (+/- 30 minutes) on weekdays AND weekends is also essential to creating a healthy internal clock and optimizing sleep quality. Choose a hour-long window of time for your bedtime and waketime that feels natural for your body and allows for 7-9 hours in bed per night (such as a 9:30-10:30 PM bedtime and 5:30-6:30 AM waketime).