Natural light streams in through the many windows of the Henry A. Jordan M ’62 Medical Education Center.
Many of today’s buildings incorporate much more glass and natural light into their designs than in the past. For example, Penn Medicine’s Henry A. Jordan M ’62 Medical Education Center, and the Pavilion, now under construction, both feature entire walls of windows that allow natural light to stream in. While this is clearly an aesthetic choice, it’s also a healthy one.
Our circadian rhythms (aka, internal clocks) need exposure to full spectrum natural light to stay in sync with the external environment. Natural light is made up of several wavelengths, each a different color. Red is the longest; violet the shortest. When all the waves are seen together, they make white light.
“Light is our biggest time cue,” said Annika Barber, PhD, a postdoctoral fellow in Chronobiology, but “blue light is particularly important.” Special cells in our eyes use melanopsin, a pigment especially sensitive to blue wavelengths, to transmit information to the suprachiasmatic nucleus (SCN), a part of the brain’s hypothalamus which is responsible for controlling circadian rhythm. “The light input resets the SCN daily, telling the brain: It’s morning!”
As the master pacemaker, the SCN then “communicates” this signal to all of the body’s tissues so they can be synchronized and perform their functions at the optimal times of day. “It’s important for all our internal clocks to tell the same time. It’s how we anticipate daily changes in our environment,” Barber said. Without daily exposure to natural light, health issues can develop, including reduced attention span, depressed mood, and possibly weight gain. “Even if you’re exercising and eating the same amount, if there’s no strong light stimulus resetting your body’s clocks, then your metabolic clock might be off and not processing food you eat as efficiently… resulting in inappropriate fat storage.”
A person needs at least 30 minutes at 1,000-lux (how light is measured) to start the circadian process, which is fairly easy to get outside. Although levels of sunlight vary, in the morning sun, you can get a whopping 100,000 lux! But even on an overcast day, you’re getting 1,000. If driving or walking to work is not part of your daily commute, working by a window (or within 20-25 feet) will also provide the necessary exposure.
However you choose to get your lux, it’s important to note that the best way is from a natural source. Most fluorescent light does not include the blue wavelength, which kicks off the daily wake-up call. Using a light meter, Barber measured three locations in her workspace. Light pouring down on the windowsill measured 5,000 lux. On a desk near the window, it fell to around 700 but in an office with only fluorescent light, the meter showed less than 250 lux. Barber said that while fluorescent lighting has improved in terms of expanding the wavelengths of light, “when it comes to our circadian rhythm, we’re not quite there. When you work indoors in low-light conditions, you’re not getting a normal light distribution to keep your clocks in sync.”
Luckily, our internal clock is “robust,” she said. “It will try to work with whatever you give it. If you go outdoors on weekends, it will re-entrain [reset] your clock back to normal.” That will keep you going Monday and Tuesday, but by Wednesday, “you’ll start to feel a slump.”
While access to bright light is critical during the day, getting too much light – especially blue-spectrum light – in the evening is not good. “It’s good that, when you leave work, the intensity of light is less. You want your clock to taper down,” she said, noting that exposure to bright light late in the afternoon disrupts melatonin production, which our body needs to get ready to sleep. This includes the artificial blue light that’s emitted by electronic devices – like smartphones, laptops and tablets – which also suppresses the release of melatonin. According to the National Sleep Foundation, “The more electronic devices that a person uses in the evening, the harder it is to fall asleep or stay asleep.” In addition, when used at bedtime, these devices “reduce the total amount of REM sleep, and compromises alertness the next morning. Over time, these effects can add up to a significant, chronic deficiency in sleep.”
For people without regular access to a window during the day—such as those who work in labs or in offices below ground level -- there are still ways can still get the necessary light. For instance, go out for a 20-minute walk over lunch. Both the exposure to the outside light and the exercise will do you good! Can’t get outside? Eat lunch by a window.
Or get a light box, typically used to treat seasonal affective disorder, for your workspace. People living in countries that have very short days during the winter -- and higher rates of SAD-- use this type of therapy to help reverse the impact.
But only use the light box in the morning, Barber stressed. “You don’t want to be telling your internal clock that it’s morning at 3:30 in the afternoon,” she said. “The body will take this as a wake-up call … but at the wrong time!”