Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Do you stay up late at night on your computer or watching TV? Professor Vishton explains how this is disrupting your sleep. Luckily, there’s a simple solution.
Before you go to bed, you can take steps to ensure an effective night of sleep. First, Professor Vishton recommends that you avoid bright lights, particularly blue light, for several hours before you go to sleep.
Bright incandescent or fluorescent lights can be bad. Computer screens, iPad screens, and modern LED television screens are even worse.
There are three things to understand about how the brain and our eyes regulate our sleep. First, proper sleep relies on a 24-hour timing cycle—a circadian rhythm—maintained by your brain, particularly the part of the brain that regulates sleep function.
Second, the clock in your head runs slow. Fortunately, the clock has a natural mechanism for setting the right time every day. Third, a lot of blue light doesn’t look blue.
Our Internal Clock
Let’s start with the human circadian rhythm and the internal clock inside your brain. The clock itself is a tiny region called the suprachiasmatic nucleus—it contains about 20,000 neurons and is located in the hypothalamus, right above the optic chiasm.
The optic chiasm is the place where your optic nerves from your two eyes come together. Every evening, the clock triggers a cascade of physiological events.
It causes the release of melatonin, a hormone that works to lower your heart rate and body temperature and eventually bring on sleep. There’s one problem with the clock—it runs about one hour slow each day.
Studies have been run in which participants lived in an environment without external time cues. They were sequestered in an isolated basement living area. All clocks were removed, and care was taken to remove any other time cues as well.
The participants in these studies were allowed to turn the lights on and off whenever they wanted as long as they stayed in the living area. When they felt it was time to go to sleep, they could shut the lights out and do so.
First, the participants slept for about eight hours a night. Left to our natural inclinations, the human body wants those eight hours.
Second, each eight hours of sleep started about 25 hours after the last one started. The human circadian rhythm clock directed the normal sleep pattern, but it waited consistently longer than 24 hours from cycle to cycle.
Blue Light and Sleep
If our bodies want to live on a 25-hour cycle, why don’t we all do so? The suprachiasmatic nucleus has a reset mechanism: sunlight. We wake up and, sometime shortly thereafter, most people see some sunlight.
As we do, it resets the clock. After a day has passed, the sun starts to set, and the light gets dimmer. The clock starts to run down and start up the sleep cycle. When the sunlight hits it the next day, it starts all over again.
In 1998, researchers discovered a type of receptor in the human retina that’s critical to this process. These receptors are called melanopsin retinal ganglion cells, which connect almost directly from the eye, down the optic nerve, and then to the suprachiasmatic nucleus.
These particular receptors are most sensitive to blue light. If you shine a purely red light on your eyes, it will activate these receptors a little, especially if it’s very bright. However, even a small amount of blue light will cause these receptors to send a burst of activation from the eye to that internal sleep clock located above the optic chiasm.
It’s also important to note that many colors—not just blue light—contain blue light wavelengths. Sunlight—even bright white sunlight—contains an evenly distributed mix of many wavelengths of light, including blue.
It’s the blue range wavelengths that matter, but even when you’re looking at something that isn’t blue, especially in conditions of bright illumination, there’s often a blue wavelength component to it. When this blue frequency light strikes the receptors, it disrupts the suprachiasmatic nucleus function.
If you look at a computer screen, it greatly reduces your brain’s release of melatonin. It’s like you’ve taken the clock that was running slow already and grabbed the second hand to make it stop completely for a while.
Blue Light Blockers
If you must look at a screen at bedtime, there’s another solution: sunglasses. There are some pricey sunglasses on the market that specifically block blue light frequencies, but most orange-tinted sunglasses will work almost as well.
You might feel silly wearing sunglasses while you watch TV before bed, but there’s good evidence that they work. Your melatonin levels will rise more normally, and you’ll drop off to sleep more quickly.
There’s a flip side to this tip that you might find useful about eight hours later. Look out the window at the blue sky first thing in the morning.
Or, if your daily schedule calls for you to rise before the sun, you can downregulate your melatonin production, and wake up more quickly, by staring at a computer screen or television. Broad spectrum or bluish illumination will reset that clock and get your brain active and on its way.
Eight hours of sleep per night is important to maintaining optimum brain function. Avoiding computer screens in the evening or using blue-light-blocking glasses are simple ways to align with your internal clock so you can get to sleep.
This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.
Peter M. Vishton is Associate Professor of Psychology at William & Mary. He earned his PhD in Psychology and Cognitive Science from Cornell University. Before joining the faculty of William & Mary, he taught at Northwestern University and served as the program director for developmental and learning sciences at the National Science Foundation.