Today’s blog post is sponsored by Connet Laser– a leading manufacturer of fiber lasers and amplifiers.
Seasonal Affective Disorder
Especially in these pandemic times, getting outside has been advertised as more important than ever. Being outside gives humans access to vitamin D, which is absorbed through the skin. Vitamin D can help prevent bone loss and also decreases the risk of some cancers and heart diseases. Seasonal Affective Disorder (SAD), more colloquially discussed as “seasonal depression” is defined as a major depressive disorder with seasonal patterns, most often during the winter months. This most often affects people in higher latitude areas, where nights are long and natural light is sparse. Two theories are common in the reasoning behind SAD. The first is that decreased exposure to natural light can change sleeping patterns and hormones. The second is that the brains of individuals with SAD have light dependent chemicals that are more affected by the change of light. Both theories express the importance of natural light exposure.
“Smart” Lighting In Swedish Classrooms
A change in sleep patterns is one of the biggest issues related to season mood changes, and can lead to seasonal depression. The circadian clock is the biological cycle that makes humans feel natural occurrences, such as sleep and hunger. During winter, the circadian clock changes, and therefore changes the body’s usual functions. The most popular theory about why the circadian clock is altered in the winter is the “phase shift hypothesis.” The colder, shorter days leave the body thinking it is a different time of day than it actually is, which leads to melatonin release at incorrect times. Melatonin is a hormone which causes sleep and therefore controls the sleep cycle. This means that during winter, people may get less sleep, causing lower mood levels.
BrainLit is a Swedish company that develops lights to mimic the circadian clock. BioCentric Lighting is their lighting solution which changes the intensity, wavelength, direction, timing, and duration of their LED lights to best align with human’s biological clocks. The system is a smart system, controlled by a light controller, it gets information from sensors to control the different lights. Higher alertness, better sleep, and increased productivity are some of the reviews that people have experienced. BioCentric Lighting are present in public areas such as schools and offices, places where people spend a majority of their day inside.
Solutions in the Subway
Researchers at the KTH Royal Institute of Technology in Sweden looked into the effects that subway lighting has on the circadian rhythms of the body, since humans are not being exposed to as much natural light during the long winter night. The paper is titled, “Lighting Evaluation and Design for the Stockholm Metro System Based on Current Models for Nonvisual Responses.” About a million people ride the subway system in Sweden each week, which is a significant amount considering only about 10 million people live there. As discussed in an earlier previous article on blue light effects, high energy, shorter wave length light has a greater impact on melatonin suppression. This paper studied the “non-visual” effects of subway light, which quantifies sleepiness versus alertness. The Circadian Light (CL) and Circadian Stimulus (CS) models were utilized to turn these non-visual effects into measurable numbers. The CL model is a non-linear equation that looks at how much illuminance effects the body’s circadian rhythm, by looking at melatonin levels. The CS model includes the circadian light model, but directly calculates the amount of melatonin suppression. Melatonin level is how “sleepiness” is being measured.
The average travel subway travel time in Sweden is about 20 minutes. This paper researched if this amount of time spent under light is enough to counteract the negative effects of limited daylight, which on the shortest day only lasts 6 hours. Many of the passengers aboard take the metro in the morning and evening, or the crucial parts on the circadian clock where humans wake up or sleep. An image of the specific train car researched is shown below. 60 spots around the car were examined for its spectral power distribution and illuminance. A spectral power distribution contains all the physical properties of light, such as color. Values were also recorded for the Circadian Stimulus model for the 60 points. The spectral power distribution was graphed for all points, and it was found that all areas had nearly identical values, pointing to illuminance being the main factor for impacts on circadian rhythm.
After analyzing the illuminance data, it was found the standing areas had the highest circadian stimulus values, being the closest to the lights. The window seats have the lowest stimulus effects from the lights, being the furthest. The Lighting Research Center recommends indoor lighting has Circadian Stimulus values of at least 0.3 during the day time, and 0.1 at night, in order to have the least impact on the body’s inner workings. The window seats had an average values of 0.13, while standing areas had 0.29. The light intensity and properties do not change throughout the day. These metro lights are not stimulating enough in the morning, while too harsh in the evening. Using LEDs that change illuminance and spectral power distributions throughout the day is the solution proposed by the Swedish researchers. These lights should emit shorter wavelengths during the morning, which increase stimulating effects, and decrease it during the night.
For arctic areas, it is difficult to not feel the “winter blues” and be impacted by seasonal depression. Temperatures drop and sunlight fades, making it harder for humans to use environmental clues for natural cycles. This can lead to seasonal depression, irritability, and poor sleep schedules. Since the Swedish metro is mostly taken by people in the morning and evening, a “smarter” lighting system could greatly improve one’s day. This also applies to classrooms and offices with lighting. Bright, short wavelength light in the morning will wake a commuter up in the morning, despite it being dark outside. Lower illuminance, calmer light in the evenings will have the opposite effect, allowing someone to have better sleep after a long work day.