Blue Noon

About 4 million people live inside our planet’s Arctic Circle - an imaginary line at latitude 66°33´ North. This area includes large chunks of Scandinavia, the Siberian coastline and Alaska, as well as the northernmost regions of Canada and most of Greenland. About 10% of all the people living above the Arctic Circle live in Norway, being in turn ≈10% of the total Norwegian population. Anyone who has happened to visit Northern Norway during either the summer or winter – perhaps looking for experiencing the midnight sun or the Northern lights (aurora borealis), respectively - would have noticed that the changes in sunlight in this part of the world compared to their place of origin can be rather extreme. Indeed, for a long period during the winter season there is a complete absence of direct sunlight or a pervasive dim light, called mørketid (“dark time” in Norwegian); in contrast, in the summer months, there is continuous light as the sun remains above the horizon through the night (i.e., the midnattsol or “midnight sun” period). For example, at 69° 40´ North, in the city of Tromsø, which is one of the largest urban communities within the Arctic, the sun disappears below the horizon at the end of November, only to reappear at the end of January; whereas the whole disc of the sun remains above the horizon for 24 hours a day from the second half of May until the end of July. In contrast, in Oslo (59° 55’ North), during the same winter and summer periods, the duration of daylight and of darkness ranges, respectively, from 5 to 6 hours each day.

In the northern hemisphere of Earth, outside the Arctic region is impossible to experience sunlight coming from the North, as it happens for two months in Tromsø during the summer or, in contrast, to experience “Darkness at Noon”, as it happens in the same place in the winter. In theory, during a whole year the total exposure to direct sunlight should be the same as anywhere else on Earth, the only difference being in how sunlight gets distributed along the whole year at each location. People living at the equator receive identical doses of 12 hours of sunlight per day - every single day of the year - but this proportion changes continuously the more one approaches the polar areas and eventually reaches all-or-none doses during the summer and winter months respectively, as it happens in Northern Norway. In truth, sunlight is not a commodity that is equally distributed on Earth during the year. Surprisingly, it is the Arctic (or Antarctic) regions that receive the longest exposure to light during a period of a year, not the tropics or equator. In fact, it is at latitudes between 60◦ and 80◦ that the cumulative length of light in the sky reaches its maximum (Ørbæk, 2006). The reason for this inequality is due to the phenomenon commonly called “twilight” or the presence of sunlight despite the sun is hidden below the horizon a few degrees (the so-called civil twilight corresponds to a position of the sun of ≈ - 6º in relation to the horizon). What is special in the Arctic is that the winter twilight can last for hours instead for just a few minutes as in most of the inhabited world. A remarkable visible effect of such an extended twilight is the prolonged presence in the sky of that range of the color spectrum of sunlight that is more prone to be scattered when reaching the Earth’s atmosphere from below the horizon; that is, the shortest wavelengths in the sunbeams or the blue and indigo bands of the color rainbow - as Isaac Newton’s classic experiments with the glass prisms had also clearly shown. Moreover, in the Arctic winter, these “blues” get further reflected by snow on the ground. Hence in the Arctic, during the winter months, the prevalent light is a blue tint that pervades the whole landscape.

Nevertheless, despite a longer exposure to light, the sunbeams reaching ground in the Arctic remain very weak during the whole year, due the inclination of Earth’s rotation with respects to the Sun and the wide distribution of the sun rays near Polar Regions, delivering less total irradiation energy per square meter than at lower latitudes. In fact, at latitudes above the Arctic Circle, although the autumn and spring seasons would have a daylight cycle that is not very different from that of central Europe, the average solar irradiation remains sensibly lower in Norway (<800 kWh/m2 ) than in Germany (1200-1800 kWh/m2).

Surprisingly, very little is known - from a science perspective - about the impact of extended periods of absence or presence of sunlight on human color vision. One would expect that the ceaseless outdoor exposure to natural sunlight during the summer months versus a reduction in energy and range of the visible light spectrum during the winter months could provoke changes in the color vision of those northerners who happen to be born in a particular season. It is known that humans are remarkably immature for an extended period after birth, so there are good reasons to think that very different light environments may have a tangible impact on development and, possibly, alterations of vision may be irreversible past a certain sensitive period.

Laboratory experiments with animals have shown that abnormal visual environments in which the animal is exposed to only one type of sensory stimulation (Blakemore & Cooper, 1970) can result in anatomical and physiological changes within the animal’s eyes and brain and affect its visual abilities. Moreover, the examination of eyes of species living in specific environments (for example, underwater) show that the maximum sensitivity of their color-sensitive cells generally correspond to the most common wavelengths of light found in their environment, while minimum sensitivities correspond to segments of the color spectrum which are rare or absent in the environment (Lythgoe, 1979).

Research on human infants has shown that color vision develops slowly but mainly within the first year of life: two-months old can discriminate reds, oranges, blue-greens and blues from a white surround but not yellow/green and mid-purple (Teller, 1998). By three or four months, infants show evidence of discriminating all colors, but the development of the ability to detect green and yellow appears to progress more slowly than other colors (Adams, Courage & Mercer, 1994).

»Research on human infants has shown that color vision develops slowly but mainly within the first year of life»

Hence, there are good reasons to expect that both sunlight deprivation and the specific changes in the color spectrum of ambient light could affect human color vision, especially when these occur during early infancy. If color vision is still developing after birth until around the first quarter of first year of life, then the variation in color experiences during these initial months of life could permanently change people’s color vision, depending on the level of light stimulation as well as the colors prevalent during the first months from birth. Moreover, during the winter months of Northern Norway, where many people live in urban areas, everyday activities are typically conducted under artificial illumination that was provided until quite recently exclusively by electric bulbs or neon tubes. In general, artificial light can rarely approximate the energy over the color spectrum of sunlight. Hence, the indoors, artificially illuminated environment, would also be expected to have an impact on color experience to a degree that is radically different from that most humans typically experience, since in most environments sunlight is present on a daily basis and also it is distributed more evenly across seasons.

»The hypothesis of the study was straightforward: A lack of an adequate amount of natural sunlight stimulation for an extended period of time during winter would negatively affect the development of color vision.»

A study by Laeng and colleagues (2007), conducted at the University of Tromsø and published in the journal Vision Research, specifically aimed to measure individual differences in color vision among adults, all residents of the same northern latitude at the time of testing, but who were born either below or above the Arctic Circle. Hence the study looked for the presence of measurable differences in color vision in northerners and southerners of adult age, although such differences are likely to be caused during infancy. Crucially, the season of birth of each individual was taken into account when comparing the two groups of participants who were born either below or above the Arctic Circle. The hypothesis of the study was straightforward: A lack of an adequate amount of natural sunlight stimulation for an extended period of time during winter would negatively affect the development of color vision.

However, it was also expected that the increased use of artificial lighting, consisting of incandescent light or tungsten lamps (mainly in private buildings) and fluorescent lamps (mainly in public buildings), may compensate to some extent for the reduction in sunlight during winter. Yet, the most common types of artificial lighting cannot entirely substitute the strength of the energy from sunlight and provide only a rather limited range of the sunlight’s composition of wavelengths that would naturally stimulate the human eye (Livingstone, 2002).

One of the study’s main expectations was that the perceptual process that is most immature at birth (for example, detecting yellow or green) would be most likely to be disrupted by reduction in light energy during development. However, additional considerations about the prevalent light range above the Arctic Circle - in particular the long exposure to the dim twilight at latitudes between 60◦ and 80◦ - also lead to expecting an increased sensitivity for colors present at twilight, like indigo and purple. Based on the above considerations about outdoor (natural) light with the protracted use of indoors (artificial) lighting, it was then expected that error rates in the color vision test should occur for northerners with those colors that are least compensated by incandescent or fluorescent artificial lighting; that is, the blue-green shades of color.

In the study, a total of 260 Norwegian individuals, all residents of the city of Tromsø for at least one year, volunteered to have their color vision checked with a specialized and standard test (the Farnsworth-Munsell 100 Hues test). Each participant’s task was to arrange or re-order movable color chips, resembling the colored caps of lipstick tubes, so as to re-create as precisely as possible the correct gradual progression of colors.

»In the study, a total of 260 Norwegian individuals, all residents of the city of Tromsø for at least one year, volunteered. 125 were born above the Arctic Circle and 135 born below.»

As the Figure below shows, on average, the two groups of participants (125 born above the Arctic Circle and 135 individuals born below) showed a rather different pattern of color discrimination errors. Those born inside the Arctic Circle were on average worse in discriminating greenish while showing relatively better discrimination of hues within the purple range of the spectrum compared to those born outside or below the Arctic Circle.

In contrast the two groups did not differ significantly for other portions of the color circle, like, like variations in orange and red colors.

The season of birth of the participants had also effects on the ability to distinguish some specific colors, but only for those individuals born inside the Arctic Circle, since there was an increase in the errors for green-blue and yellow-green colors by northerners born in the winter compared to those born in summer but no difference for the southerners based on the season of birth. Both northerners and southerners born during the autumn and spring seasons showed no differences in the color test, which makes sense given that both seasons have no overall difference in average daylight at different geographical locations and therefore these people would have experienced similar amount of light exposure and color variations in the environment, regardless of the geographical location of their birth place. Crucially, individuals born above the Arctic Circle and in the summer had significantly lower overall error scores compared to individuals born below the Arctic Circle; thus, depending on one’s date of birth, growing up in the northernmost regions can also positively affect color vision.

»Crucially, individuals born above the Arctic Circle and in the summer had significantly lower overall error scores compared to individuals born further south; thus, depending on one’s date of birth, growing up in the northernmost regions can positively affect color vision.»

Moreover, about 32 individuals born in the Arctic who participated in the study belonged to families who had moved to a residence below the Arctic Circle during their childhood (i.e., age < 10 years). This smaller group also differed from the group of individuals born below the Arctic Circle in showing more green-blue discrimination errors and fewer errors for purple colors. Remarkably, the number of years spent in the birthplace had no relationship with their errors with the green-blue colors. These findings allow the conclusion that permanence within the Arctic during the first months of life may be sufficient to alter color vision into adult life.

Thus, the study was successful in revealing differences in color vision between southerners and northerners and, in the latter group, color vision changes were dependent on being born in a specific season of the year. However, it is important to point out that these differences in color vision, although they are measurable and clear, fall within what is considered a normal range of color abilities, at least as measured with the FM100 test. A main conclusion of the study is that the environmental impact on color vision acts early in infancy. Indeed, the first months of life for those born in autumn and winter would coincide with the least exposure to direct sunlight (mørketid) and the most exposure to twilight. Such an exposure to nearly monochromatic natural ambient light (twilight) could have been the main causal factor in selectively improving color visual discrimination for the colors that are prevalent in the ambient. The best performance in the test was shown by individuals born in the summer and above the Arctic Circle, which suggests that prolonged levels of light stimulation in this group (midnattsol) can cause small enhancements of the typical development of color vision. Hence, the continuous presence of sunlight in the summer months can influence the developing visual mechanisms.

In addition, electric artificial lighting supplements the lack of natural light during mørketid. Changes in the ability to distinguish specific colors reflect the combined effect of the narrowing of the spectrum of natural light towards the short wavelengths combined with the concomitant, protracted, exposure to (mainly) incandescent light. Artificial lighting of tungsten lamps has a relative energy that is lowest for short-wavelengths and highest (approximating the energy of natural sunlight) for the long wavelengths, like reds. Instead, fluorescent lamps have an irregular profile of relative energy over wavelengths and they approximate sunlight’s energy for wavelengths only within the ‘orange’ part of the spectrum. Thus, the long exposure to indoors lighting, during the winter period seems to play another crucial role to color vision abilities in adult age. Indeed, the largest error in arranging the colored chips of the test occurred in those regions of the visible color spectrum where the energy of incandescent or fluorescent light is poorest compared to sunlight energy; that is, for blue-green and green-yellow. In contrast, the unusually high exposure to twilight above the Arctic Circle provides a light environment that is beneficial to visual discriminations of the shortest wavelengths of sunlight like the indigo-purple shades of color, which can so beautifully color the sky of the North during the winter.

»The unusually high exposure to twilight above the Arctic Circle provides a light environment that is beneficial to visual discriminations of the shortest wavelengths of sunlight like the indigo-purple shades of color.»

A final consideration can be based on the common lore that different groups of people prefer different colors. For example in Norway, according to statistics of the Norges Automobil-Forbund (NAF), the color red is the third most chosen color for a car by women but the seventh choice for men’s cars. Given all of the above described differences in color vision, should we also expect that northerners prefer or abhor certain colors compared to the southerners? Maybe not, since the differences in vision appear to be subtle and may make little difference with regards to the enjoyment of color. Yet, when visiting the North, one cannot fail to notice the strong colors of the paints used on houses compared to those in the South where white prevails.

References

Adams, R. J., Courage, M. L., & Mercer, M. E. (1994). «Systematic measurement of human neonatal color vision». Vision Research, 34, 1691-1701.
Blakemore, C., & Cooper, G. F. (1970). «Development of the brain depends on the visual environment». Nature, 228, 477-478.
Farnsworth, D. (1957). The Farnsworth-Munsell 100-Hue Test for the examination of color discrimination. Baltimore, MD: Munsell Color Company, Inc. Laeng, B., Brennen, T., Elden, Å., Paulsen, H.G., Banerjee, A., & Lipton, R. (2007). «Latitude-of-birth and season-of-birth effects on human color vision in the Arctic». Vision Research, 47, 1595-1607.
Livingstone, M. (2002). Vision and art: The biology of seeing. New York: Abrams.
Lythgoe, J. N. (1979). The ecology of vision. New York: Oxford University Press.
Teller, D. Y. (1998). «Spatial and temporal aspects of infant color vision». Vision Research, 38, 3275–3282.
Ørbæk, J. B. (2006). «Blue light in the arctic: Polar day, polar night and the low arctic sun». In J. B. Ørbæk & A- Brekke (eds.), Arctic lights, pp. 24-30. Tromsø Museum, University of Tromsø, Norway: Lundblad Media.