Unlocking the Mysteries of the Purkinje Effect During a Total Solar Eclipse

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Over two centuries ago, physiologist Jan Evangelista Purkyně observed that red flowers appeared bright carmine during sunny days but changed to a deep muted hue at nighttime.

The Purkinje effect, now a well-known phenomenon, explains why colors appear differently depending on the amount of light present. In low light conditions, bright reds may appear darker and faded, sometimes even appearing almost black. On the other hand, blues and greens tend to become more vibrant. The occurrence of a total solar eclipse provides a perfect opportunity to witness this color shift.

The transition of the Purkinje effect typically happens gradually as day transitions into night. Our eyes, equipped with two types of light-sensitive receptors, begin to adjust from using cone cells that provide color information in bright light to relying on rod cells in low light. Rod cells are more sensitive to blue-green wavelengths. Will Snyder, the manager of the James S. McDonnell Planetarium at the Saint Louis Science Center in Missouri, explains this process.

The sun's corona is visible as the moon passes in front of the sun during a total solar eclipse at Big Summit Prairie ranch in Oregon's Ochoco National Forest near the city of Mitchell on August 21, 2017. The Sun started to vanish behind the Moon as the partial phase of the so-called Great American Eclipse began Monday, with millions of eager sky-gazers soon to witness "totality" across the nation for the first time in nearly a century. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP via Getty Images)

During a total solar eclipse at Big Summit Prairie ranch in Oregon's Ochoco National Forest near the city of Mitchell on August 21, 2017, the sun's corona was visible as the moon passed in front of the sun. The Sun started to vanish behind the Moon as the partial phase of the so-called Great American Eclipse began. Millions of eager sky-gazers were soon to witness "totality" across the nation for the first time in nearly a century. / AFP PHOTO / Robyn Beck(Photo credit should read ROBYN BECK/AFP via Getty Images)

Robyn Beck/AFP/Getty Images

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As the total solar eclipse approaches on April 8, the moon will gradually cover the sun, causing a reduction in the amount of light reaching the Earth. This will result in a color perception similar to dusk, with a noticeable decrease in contrast as the transition from daylight to evening-like light occurs rapidly during the eclipse.

Snyder explained that the Purkinje effect is not a real change in colors during an eclipse. It is simply how our eyes and brains perceive light. As the sky darkens during an eclipse, our eyes struggle to adjust quickly enough, causing red objects to appear less vibrant compared to blue or green objects.

When preparing for an eclipse, it is important to consider what to wear. Since the Purkinje effect can make red colors appear dull, it may be a good idea to choose clothing in brighter shades of blue or green to stand out more during the event. This way, you can fully enjoy the unique experience of witnessing a celestial phenomenon like a solar eclipse.

During the eclipse twilight, our eyes will quickly adjust to the changing light conditions. Instead of the usual slow transition from cones to rods taking up to 45 minutes, both will start working together. This means that in low light, cones won't pick up colors well, but rods will detect blues and greens more easily, making them stand out.

This simultaneous activity of cones and rods during the eclipse twilight is called mesopic vision. This shift is most noticeable right before totality, when the moon fully covers the sun. During mesopic vision, everything may appear to have a gray or "sepia tone," as noted by the Saint Louis Science Center.

For those not in the path of totality, the effect of the eclipse may still be visible depending on how dark it gets, explained Dr. Grady Rylander III, an ophthalmologist and professor at the University of Texas at Austin. During a partial eclipse where more than half of the sun is obscured, daylight will appear dimmer, as noted by The Planetary Society.

To observe the Purkinje effect, individuals must remove their eclipse glasses, but only when looking at their surroundings, advised Rylander. It is crucial to never gaze directly at the sun without protective eyewear to avoid permanent damage to the retina. "The Purkinje effect can be seen when observing objects around you during the eclipse, not the sun itself," Rylander emphasized in an email.

For a more vibrant viewing experience of the phenomenon, Snyder recommends wearing red and green to enhance the color contrast as the event unfolds.

FILE - People gather near Redmond, Ore., to view the sun as it nears a total eclipse by the moon, Monday, Aug. 21, 2017. The April 8, 2024 total solar eclipse in North America first hits land at Mexico’s Pacific coast, cuts diagonally across the U.S. from Texas to Maine and exits in eastern Canada. (AP Photo/Ted S. Warren, File)

People in Redmond, Oregon gathered to watch the sun being covered by the moon on August 21, 2017. The next total solar eclipse in North America will occur on April 8, 2024. It will start at Mexico's Pacific coast, then move diagonally across the United States from Texas to Maine, before ending in eastern Canada. The event will be a spectacular sight for all to see.

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Snyder mentioned that in April, Christmas shirts with red and green stripes can be interesting to look at. The combination of these two colors side by side can create a visually appealing effect.

He explained that this phenomenon cannot be captured on cameras because it is a result of how human eyes interpret light.

"Total solar eclipses are exciting because they are relatively rare and come with many cool phenomena," Snyder explained. "This effect just adds to the list of reasons why eclipses are so fascinating."

Editor's P/S:

The Purkinje effect, a fascinating visual phenomenon, reveals how our perception of colors shifts with varying light conditions. During a total solar eclipse, the drastic reduction in sunlight triggers a transition in our eyes from relying on cone cells (responsible for color vision in bright light) to rod cells (more sensitive to blue-green wavelengths). This physiological adjustment leads to a noticeable change in the way colors appear, with red hues becoming muted while blue and green shades become more prominent.

The Purkinje effect not only offers a glimpse into the intricate workings of our visual system but also provides an opportunity for memorable experiences during celestial events like solar eclipses. By understanding this phenomenon, we can enhance our enjoyment of these awe-inspiring events. Choosing clothing in shades of blue or green, for example, can maximize the contrast and create a more visually captivating experience. Additionally, being aware of the Purkinje effect can help us appreciate the unique color transformations that occur during these rare occurrences, making them even more unforgettable.