Sleep is important for health and weight. Sleep, like many other processes, is governed by the brain. In particular, the brain contains a “clock” that resides primarily in the suprachiasmatic nucleus (SCN). This clock has a cycle of approximately 24 hours, and regulates other parts of the brain that effect the onset and termination of sleep. The SCN is a tiny nucleus that’s positioned just above the optic chiasm, the place where the two optic nerves cross. These are the nerves that transmit information from the retinas to the brain. Not surprisingly, the SCN receives direct input from the retinas. Also not surprisingly for a species that lives by the day-night cycle, the human SCN clock is set primarily by light.
This poses a problem for modern humans, who expose ourselves to artificial light long after the sun has gone down. This light essentially tells our SCN clock it’s still daytime, making it more difficult to sleep at night and more difficult to get up in the morning. This is clearly evident because nighttime light suppresses the secretion of the sleep hormone melatonin by the pineal gland, which is under the control of the SCN (1, 2).
Interestingly, the photoreceptors in the retina that project to the SCN are most sensitive to blue light (1, 2). This may be because midday sunlight is more blue than light around sunrise and sunset, and is therefore a better cue for setting the clock. In any case, this peculiarity of human physiology gives us the opportunity to minimize the negative impacts of evening light by shifting it to a less blue spectrum.
Computer monitors are one of the most problematic sources of light because they’re bright and often contain a lot of blue light. One solution is to wear blue-blocking glasses such as the inexpensive Uvex SCT Orange
model. I’ve been using these for about a year and they work well. I notice myself feeling more tired almost immediately after putting them on. Controlled trials have confirmed that blue-blocking glasses completely restore melatonin secretion (3
), presumably eliminating the effects of artificial light on the SCN clock.
Another great tool is F.lux
, a free computer program that automatically changes your monitor’s color spectrum based on the time of day. I’ve been using this for about two years, and previously felt that it wasn’t able to remove enough blue light to be very useful. I recently realized that they upgraded it in a way that makes it much better. If you pull up the program, click on the three horizontal lines to the right of the settings menu, and scroll over the “lighting at night” menu, you will see seven options for color temperature ranging from “sunlight” to “ember”. I’ve found that when I dim my monitor, the ember setting is equivalent to wearing blue-blocking shades while I use my computer. In fact, I’m feeling sleepy right now as I write this.
In the Ideal Weight Program
, we focus on improving sleep quantity and quality in part by using skillful light exposure to naturally guide the SCN clock to a healthy day-night cycle. F.lux is a useful tool that we highly recommend.
Written by Stephan J. Guyenet, Ph.D., co-developer of the Ideal Weight Program