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Mood Lighting

September 5, 2022

Just a few decades ago, everyone read from print media, and display management was easy. If the room was too dark for reading, you needed to turn on a light. Today, it's possible to read from a tablet computer in a totally dark room. research was done in the early days of computing to determine which text mode was more readable, black characters on a white background, as in a printed book, or white characters on a black background, commonly called dark mode. Having a background that matched the room background was found to be beneficial; so, your tablet display should have white characters on a black background when reading in a dark room. I personally find that annoying, and there's the further problem of how images in dark mode are rendered.

A median effort, called Night Shift, was introduced by Apple a few years ago. This mode lowered the color temperature of the display by shifting it towards yellow, thereby reducing blue. All light, but especially blue light, suppresses melatonin biosynthesis,[1] so the conjecture was that such a color shift will aid sleep after nightime reading. However, a recent study showed no differences in sleep outcomes attributable to Night Shift, and not using a display resulted in better sleep quality than using a Night Shift display.[2]

The CIE 1931 x,y chromaticity space

The CIE 1931 x,y chromaticity space, a typical representation of the visual colors.

The quality of a display is measured by how much of an area of the space can be represented, a so-called color gamut. The unusual word, gamut, means "the complete range or scope of something."

This diagram shows also the black-body colors at various temperatures. The color temperature of the Sun is about 5780 K.

The CIE 1931 color spaces were designed by the International Commission on Illumination (Commission Internationale de l'éclairage). They were the first quantitative links between the wavelengths in the visible spectrum and the perceived colors in human color vision.

(Wikimedia Commons image by PAR. Click for larger image.)

Human vision is amazing, as evidenced by the fact that most people can discern a candle flame at 48 kilometers (30 miles) on a clear, dark night.[3] As most of us will remember from our high school biology class, night vision is enabled by retinal rods, and color vision is enabled by retinal cones. The human eye has three types of cone cells, and each of these can discern about 100 different color shades; so, humans can distinguish about a million colors.[3]

Some people, mostly women, have a genetic mutation for a fourth cone cell. In theory, these tetrachromats can see 100 million colors. Color-blind people (dichromats) have just two types of cone cells and presumably can see just 10,000 colors.[3] I worked with a laboratory technician who was "doubly-cursed" in being both left-handed and color-blind (left-handedness is completely accepted today, but not in years past). How can I not include a mention of one famous left-handed individual, Ned Flanders. Some people who have had cataract surgery in which the eye's normal lens is replaced by an artificial lens have reported the ability to see ultraviolet light.

Nearly all computing devices display colors by a simple technique in which the values of the primary colors, red, green, and blue, are expressed as 8-bit values. This 24-bit representation in which 16,777,216 colors are displayed is known as true color, and it's far in excess of the typical million colors of human vision.

Parrot, Eastern Rosella (Platycercus eximius) female

Sometime in the history of computers, images of parrots became associated with color displays, a likely consequence of their colorful plumage.

Shown is an Eastern Rosella (Platycercus eximius) female parrot from Tasmania.

(Wikimedia Commons image by JJ Harrison. Click for larger image.)

Now that we understand the bad affects of lighting color, is there any way that lighting color can enhance mood? That's the question researched by a team of scientists from the European Space Agency (Netherlands), the University of Leeds (Leeds, UK), the Hochschule für Medien, Kommunikation und Wirtschaft (Berlin, Germany), the Xiangtan University (Xiangtan, China), Leiden University (Leiden, Netherlands), Vrije Universiteit (Amsterdam, Netherlands), and Xiangtan Central Hospital (Xiangtan, China). [5-6] Their purpose was to address the psychophysiological state of crews on manned space missions in which they live in a confined technological environment devoid of the variety and variation they had on Earth.[5-6]

Previous studies, such as the joint National Science Foundation/NASA Shared Cognitive Architectures for Long-term Exploration project and NASA's Extreme Environment Mission Operations project, have found that crew members on long-term missions are extremely susceptible to psychological problems. One contributing factor is the visual monotony and monochromatic coloring of the environment.[6] At the inception of the International Space Station, both NASA and the former Soviet Space Agency believed that psychological problems would be a factor in the success of such long-term space missions.[5]

In deep space missions, the isolated and confined environment aggravates the crew's anxiety, irritability, and depression.[5] Furthermore, signal propagation delays will make astronauts feel the anxiety of being far away from Earth.[5] This stress sometimes manifests itself in such things as unresponsiveness, intermittent mania, and crying.[5] As previously mentioned, light suppresses melatonin levels, and the color of light can have a significant role in emotional regulation and cognition.[5] In one study, a red room caused a lowered of the heart rate compared to non-colored room, and a blue room had a relaxing effect on study participants compared with the red room.[5] For astronaut health and safety, lighting in support of both circadian regulation and psychological issues should be considered.[5]

The goal of the study was to test whether multicolored lighting can improve a person's psychological state in an isolated and confined environment over a period of seven days.[5] The study was conducted at Xiangtan Central Hospital in Xiangtan, China on ten healthy male and ten female's study participants of Chinese nationality from Xiangtan University in their twenties.[5] The isolation rooms, 3.5 meters long, 3 meters wide, and 2.2 meters high, were furnished with a chair, a table, a bed, and a bedside table.[6] The walls and the ceiling were painted white, the floor was dark gray, and the door and furnishings were a light wood color.[6]

The participants were randomly divided into two groups of ten each, one group (the control group) was exposed to a static, monotonous white interior, while the test group was exposed to multicolored lighting randomly changed every three hours.[5-6] The multicolor light source was a Philips Hue Bluetooth wireless bulb, capable of displaying 16 million colors, placed in the middle area of the room.[6] The participants were not allowed to use mobile phones, computers, televisions, or iPads, but they could read paper books, and their psychological state was tested on the first day, the fourth day, and the seventh day.[5-6]

Emotional response to colored lights

Positive and negative emotional response during the multicolored lighting study for the test and control groups. The control group response, in red, is worse than that of the group exposed to the multicolored lighting. (Space: Science & Technology image.[6] Click for larger image.)

At the final day of the experiment, the anxiety level for both the test and control groups was significantly higher than that on the first day.[6] The participants' negative emotions and anxiety increased to the fourth day, and then plateaued, with the control group plateauing at a higher level (see figure).[5] It was concluded that multi color lighting alleviated the anxiety and negative emotions caused by isolation and confinement, and a random change of light color appeared to counteract the monotony of the isolation.[6] Such a simple palliative would be useful in future space exploration.[6] This may be the reason for unexplained purple wigs of the uniform of the female astronauts in the 1970s UFO television series by Gerry Anderson and Sylvia Anderson.


  1. Kathleen E. West, Michael R. Jablonski, Benjamin Warfield, Kate S. Cecil, Mary James, Melissa A. Ayers, James Maida, Charles Bowen, David H. Sliney, Mark D. Rollag, John P. Hanifin, and George C. Brainard, "Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans," Journal of Applied Physiology, vol. 110, no. 3 (March 1, 2011), https://doi.org/10.1152/japplphysiol.01413.2009. This is an open access article with a PDF file here.
  2. Kara M. Duraccio, Kelsey K. Zaugg, Robyn C. Blackburn, and Chad D. Jensen, "Does iPhone night shift mitigate negative effects of smartphone use on sleep outcomes in emerging adults?", Sleep Health, vol. 7, no. 4 (August 2021), pp. 478-484, doi:10.1016/j.sleh.2021.03.005.
  3. W. D. Wright, "A re-determination of the trichromatic coefficients of the spectral colours," Transactions of the Optical Society, vol. 30, no. 4 (March, 1929), pp. 141-164, https://doi.org/10.1088/1475-4878/30/4/301.
  4. Adam Hadhazy, "What are the limits of human vision?", BBC, July 27, 2015.
  5. Ao Jiang, Irene Lia Schlacht, Xiang Yao, Bernard Foing, Zhixiong Fang, Stephen Westland, Caroline Hemingray, and Wenhao Yao, "Space Habitat Astronautics: Multicolour Lighting Psychology in a 7-Day Simulated Habitat," Space: Science & Technology, vol. 2022 (April 9, 2022), Article ID 9782706, pp. 1-11, https://doi.org/10.34133/2022/9782706. This is an open access article with a PDF file here.
  6. How scientists tested the effect of multicolor lighting on improving people's psychological state, Beijing Institute of Technology Press Co., Ltd, Press Release, July 6, 2022.

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