Introduction

The visible light spectrum spans between 380 to 750 nanometers. The violet or blue light spectrum (below 450 nanometers) has a short wavelength but high energy. The red light (above 620 nanometers) has a longer wavelength but low energy. Sunlight is a polychromatic light and contains wavelengths of multiple frequencies. Monochromatic light or small bandwidth light consists of wavelengths of similar frequency.

Yung-Helmholtz trichromacy theory

The color that we perceive is largely determined by the relative contributions of blue, green, and red cones to the retinal signal. The fact that our visual system detects colors in this way was predicted by a British physicist Thomas Young who showed in 1802 that all the colors of the rainbow, including white, could be created by mixing the proper ratio of red, green, and blue light (RGB). He proposed that at each point in the retina there exists a cluster of three receptor types, each type being maximally sensitive to either blue, green, or red. Young’s ideas were later championed by Hermann von Helmholtz, an influential nineteenth-century German physiologist.

Figure 1: Visible light spectrum (credits: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html).

The retina contains photoreceptors that convert light energy into neural activities. Cones are responsible for color vision. In 1965 came experimental confirmation that there are three types of color-sensitive cones, corresponding roughly to red, green, and blue sensitive detectors. Coincidentally, RGB color coding in computer science is rooted in the way our eyes perceive colors.

Since the discovery of intrinsically photosensitive retinal ganglion cells (ipRGCs) in the human eye, an increasing number of studies have been performed to investigate the non-image forming effects of ocular light exposure on human functioning during the biological night and day. Research has established that light does not only have the potential to produce phase-shifting effects on the human circadian rhythm, but can also exert instantaneous effects on physiological arousal, neural activity, hormone production, and subjective alertness. In addition, light has also been shown to impact cognitive ability, including attention, inhibitory control, and working memory. Ganglion cells exposed for over 20 minutes to high energy blue light became activated and sent messages to the brain suggesting the wake time.

Experiments

The nature of the research was exploratory, initially without a clear research question to avoid subconscious agreements with published results. The student performed experiments on herself (referred to throughout the study as J) and her mother (referred to through the study as M). Participant M was a 53-year-old female with a history of narcolepsy. Narcolepsy is a neurological sleep disorder that affects an individual’s ability to control sleep-wake cycles, causing difficulties remaining awake and/or asleep (as in [7]). She works from home running an online business, thus this exposure to blue light was considered throughout the study. Participant J was a 23-year-old female who holds a typing job under hospital lighting, which was taken into consideration throughout the study and its effects were included in the results. Both subjects also regularly experience migraines. A migraine is a headache of varying intensities, typically characterized by an intense throbbing in the head. This pain is due to the nerve fibers of the brain blood vessels traveling within the three layers of membranes that protect the brain and spinal cord, referred to as the meninges (as in [6]). Both participants report being unable to tolerate any light during a migraine attack.

Both the student and her mother kept detailed journals, recording the date, time, and light color used, as well as a description of how they were reacting during these moments. A set of color changing light bulbs was installed in each participant’s bedroom. The light bulbs were controlled by a remote, and each color was given a number in order to avoid confusion (see Fig. 2). Figure 3 shows the light participant J was exposed to at her job at the time, which has greatly impacted her mood and perception, as noted in her journal. Subjects began by choosing the light color they preferred and noting how they felt along with the time of day used. Once the participant had gone through every light, they could begin choosing their preferred color as time went on. This process was done on a daily basis for three months.

Figure 2: Light colors in the experiment (credits Julissa Cardoza).

Figure 3: Light at work of participant J (credits Julissa Cardoza).

Results

The results show the frequency in which each light color was used throughout this experiment. The most significant outcome was the strong preference displayed by both participants for light 11 and 12, as well as natural lighting. For participant 1 (J), as is shown in figure 4, lights 1, 2, and 5-7, were only used once whereas light 3 and 9 were not used at all. The light color that was used the most throughout the study was light 11. As noted by the participant’s journals, this light was strongly preferred in the morning, combined with natural lighting, as it made it much easier to wake up early. Light 12 was preferred later in the day.

Participant 2 (M) showed a clear preference for lights 11, 12, along with natural lighting. Lights 4, 5, 7, and 8 were hardly used and lights 1-3, 6, 9, and 10 were never used during the study. Light 11 was preferred in combination with natural light, due to this specific color alleviating Participant M’s narcoleptic episodes. Light 12 was preferred later in the day.

Figure 4: Results for Participant 1 (J).

Figure 5: Figure 5. Results for Participant 2 (M).

Discussion

The results of this experiment did display some differences in light color preferences, as expected. However, the reasoning for some of these specific preferences were consistent with previous studies focusing on light color. Light 3 and 9 were not used at all by either participant, suggesting that these colors, deep blue/purple tone, could have a negative effect on perception. Lights 5, 6, and 7 were not preferred either, due to the participants reporting that the light colors felt too strong on the eyes, thus causing some minor confusion.

Participant 1 (J) held a strong preference for Light 11 throughout the day as it was reported this kept her alert during important tasks. Before beginning this experiment, she found difficulty waking up early, often struggling to wake up around 10-11 a.m. She also found difficulties in maintaining focus throughout the day without feeling drowsy. Participant 1 (J) also took regular midday naps prior to this study. All these symptoms and behaviors gradually began to disappear due to the effects of Light 11 and by the end of the study, Participant 1 was regularly waking up at 5 a.m. with full energy, without needing a nap later in the day. Taking into account the lighting shown in Figure 3, which initially caused the participant to feel sleepy at her job, she notes regaining energy upon returning home and exposing herself to Light 11. Light 8 was also found to best relieve migraines, of which the participants reported experiencing at least 1-2 times biweekly. This was the only light the participant described being able to tolerate during these migraine attacks, which was the first time she was able to tolerate any light at all.

Participant 2 (M) was found to strongly prefer using both Light 12 and Natural Outdoor Lighting together in order to stay awake throughout the day. It was found that when these lights were used together, the frequency of Participant 2’s narcoleptic episodes decreased. When this was found, we then tested the effects of being exposed to only one of these two lights. It was found that when Participant 2 was exposed to solely Light 12 or Natural Outdoor Lighting, the frequency of her narcoleptic episodes increased. It was the combination of these lights that were able to manage these episodes and keep her awake. Light 11 was also favored in order to keep focus while working on her online business. The use of Light 11 was also tested in combination with Natural Outdoor Lighting, and this combination was also found to be successful in reducing her narcoleptic episodes.

This study showed the aspects of mood and perception pertaining to sleep, alertness, calmness, and irritability. Light color had a great effect on sleep, with different colors being able to even regulate participant’s sleep and sleep disorder. Furthermore, there were consistencies found with previous studies, showing that there is a basis for furthering this experiment in a more controlled environment. A study conducted by Harvard Medical School was found to provide evidence that green light exposure is able to relieve migraine pain. This was a key observation in this study as well and is something that can be further explored. Other previous studies have found that blue light exposure blocks the body’s production of melatonin, thus preventing sleep (as in [5]). It was further proven that this aids in the prevention of narcoleptic episodes due to these effects, which was evident in what was reported by Participant 2. It is important to note this study was rather limited due to it being conducted in winter, which is known to greatly impact mood due to reduced sun exposure. The study also only had female participants. Future studies could greatly benefit from having greater participant diversity as well as repeating the experiment during another season.

In order to create a more controlled study, the best course of action to take could be focusing on one specific effect involving lights. This experiment can best be recreated focusing on participants with a history of narcolepsy or migraines in order to see if the aforementioned results can be duplicated. The more specific the research question, the better it would be for the sake of the reliability of the results. One could even further research which light is best to wake up peacefully or which color is best for winding down at night and falling asleep. A study of this nature can be done with a large group, to include both males and females as well as a more expansive age group or another self-study can be conducted. These results can be applied to an individual’s daily life in order to find their own light preferences and reap in the benefits as they go about their routine with ease.

References

[1] Rua T, de Kortb YAW., Smolders K CHJ, Chen Q, Zhou G. "Non-image forming effects of illuminance and correlated color temperature of office light on alertness, mood, and performance across cognitive domains." Building and Environment, 149 (2019) 253–263.

[2] Bear MF, Connors BD, Paradisco MA. "Neuroscience: Exploring the Brain." Lippincott Williams & Wilkins (2006).

[3] Romocean, M. "The psychological impact of Light & Color." TCP Lighting Solutions (2022); https://www.tcpi.com/psychological-impact-light-color/.

[4] Kritz, J. "Green light for Migraine Relief. Green Light for Migraine Relief." Harvard Medical (2016). https://hms.harvard.edu/news/green-light-migraine-relief.

[5] Arlene A, Elle E, T. S., S., T., C., Chris A., Amy B. C., Caldwell BM, Marcelle D, Desiree M, & Michele. "Blue Light and narcolepsy: How it can help: Falling asleep: A narcolepsy guidebook." Falling Asleep (2017); http://www.falling-asleep.com/blue-light-and-narcolepsy-treatment/.

[6] NINDS. (2023, January 20) Migraine | National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/disorders/migraine.

[7] Narcolepsy. (n.d.). National Institute of Neurological Disorders and Stroke; https://www.ninds.nih.gov/health-information/disorders/narcolepsy.