Last time, we explained how light contributes to the regulation of sleep-wake cycles by the brain. Briefly, the brain needs to synchronize its activity levels with the light levels in the outside world in order to be asleep and awake at the appropriate times. But not all light is created equal. White light consists of a broad range of wavelengths, only some of which are involved in the regulation of sleep-wake cycles. It is this insight that allows you to take action.
Short-wavelength light (that would appear blue if you saw a short-wavelength laser pointer) in particular drives the regulation of the sleep-wake cycle. This makes sense – the sky is blue and the appearance of short wavelengths at dawn would have served nicely as a wakeup signal in ancient times.
But we no longer live in ancient times – we are surrounded by a plethora of lights – light bulbx, TV screens, computer screens, cell phone screens, tablet screens, all of which are on until late into the night and all of which emit at least some short-wavelength light, some of them a considerable amount of it. Your brain systems designed to pick up on this will interpret the presence of these short wavelengths as daylight and tell the rest of the brain that it is time to rise, disrupting the sleep-wake cycle.
So what can you do?
The solution is fairly straightforward – simply remove the short-wavelengths from the mix. The remaining light will appear in an orange-amber hue, but not disrupt sleep cycles any longer, see diagram.
How does one go about selectively removing a particular range of wavelengths (short wavelengths) from the incoming light?
There are actually several options.
The most straightforward one would be to remove these wavelengths already at the source – the screen that is emitting the light. There are programs that allow you to set a time at which to start removing the short wavelengths, the most popular of which is f.lux. There is also a hardware solution – you can buy filters that cover the screen and achieve basically the same outcome. The latter might be a more flexible solution – for instance, if you want to do color-sensitive work at night, you can simply remove the screen (it is also possible to disable the f.lux program for a period of time).
Of course, screens are not the only major source of short wavelengths that disrupt the sleep-wake cycle at night. Most light bulbs also emit them aplenty, particularly newer ones – the classic incandescent light bulb releases most of its light in the long-wavelength range, which is why it has a warm, yellowish glow. The solution here is to replace your light bulbs with some that produce none or very little light in the short wavelengths, at least in strategic places, where you will see them at night. This could be particularly useful for a night light.
If you want a solution that works for light coming from screens and light bulbs, as well as any other conceivable source of short wavelength light at night, the most straightforward thing to do – if you can stand the fashion statement – is to wear goggles designed to filter out short wavelengths.
Regardless of which of these solutions you implement, the end-result is the same: Less short wave-length light reaching the back of your eye, signaling the brain that it is dark outside, allowing you to get the sleep that you need and deserve (see diagram).
However, all of this seems like a lot of effort. Why go to such lengths? Why does it matter? That’s what we’ll cover in the next part in our series on the science of sleep.