Frank Tenney Johnson and the Purkinje Shift

Having a better look at one of the reasons that Johnson’s moonlit scenes look so much more convincing than paintings that are merely dark and blue.

Planet of the Grapes

My God, I remember the first time I was assigned to paint a nighttime plein-air painting in college. It was the absolute worst. Although the painting thankfully did not survive to this day, what does survive is the horrible memory of piling one color on top of another, hoping that some combination would somehow make the scene look like “night.” I had no idea what I was doing, and by the time I finished, I had produced a wildly purple moonlit sky illuminating the most inappropriately green trees anyone had ever tried to squeeze into a night scene. My goodness, do I remember that green and purple. It looked less like a plein air study and more like a poorly executed cover of a science-fiction novel about a planet made of radioactive grapes. Ugh…

As aesthetically unfortunate as my effort may have been, the experience revealed something important: nighttime can be surprisingly difficult to capture in paint. What I have learned since those college days is that the challenge involves far more than making everything dark (or blasting high-chroma purple and green everywhere). Yet buried within that chromatic catastrophe was the germ of a legitimate intuition: a particular balance of colors really can help a painting register more as “nocturnal”. You see, the fact is that reduced illumination can lead to something far more interesting than simply darkening what we can see; it changes how our visual system responds. A convincing nocturne, therefore, may in part, depend in part on understanding what happens to our perception as light levels fall.

One artist who seemed to truly understand this better than most was Frank Tenney Johnson (1874–1939), one of the great painters of the American West. Johnson became so well known for his moonlit scenes that his distinctive approach became known as the “Johnson Moonlight Technique.” Unlike my brief excursion to the Planet of the Grapes, his paintings feel uncannily believable as moonlit scenes. So why do his night scenes feel so “correct”—and might their believability have some connection to the visual adaptation I mentioned? Let’s take a look.

Night Is Not Merely Less Daylight

It may seem intuitive to think of night as daylight with the dimmer switch turned down. However, as illumination falls, the visual system does not simply deliver a uniformly darker version of the same scene. Its sensitivity to different wavelengths of light begins to change.

Under bright, or photopic, conditions, vision is predominantly mediated by retinal photoreceptors called cones—which support our experience of color and allow us to resolve fine detail. At the opposite extreme, under very dim, or scotopic, conditions, vision is mediated primarily by the far more light-sensitive photoreceptors called rods. Between these two extremes lies mesopic vision, in which rods and cones both contribute. These categories do not have perfectly sharp boundaries, but mesopic vision is especially relevant to many twilight and some moonlit conditions that nocturne painters attempt to represent.

As illumination falls and rods contribute more to vision, the wavelength of peak luminance sensitivity shifts from about 555 nanometers under photopic conditions to about 507 nanometers under scotopic conditions—from the yellow-green portion of the spectrum toward blue-green. This change is known as the Purkinje shift. Practically, long-wavelength colors such as reds lose apparent brightness relative to shorter-wavelength colors, while blue-greens become comparatively brighter.

A familiar demonstration involves a red geranium surrounded by green leaves. In bright daylight, the red blossoms may stand out vividly against the foliage. As illumination falls, however, that relationship changes. The red flowers become progressively darker relative to the leaves—sometimes approaching black—while the green foliage remains comparatively bright. The reflectance properties of the flowers and leaves have not changed. What has changed is the light level and, with it, the way the visual system weights the light reflected from them.

Importantly, the Purkinje shift does not simply tint the visible world uniformly blue-green. It changes the relative brightness relationships among colors. At fully scotopic levels, the rich cone-mediated color vision familiar from daylight is largely absent; under mesopic conditions, some color vision remains, but the balance of brightness among different colors has changed. Night is therefore not merely darker than day. It is organized differently.

The Johnson Moonlight Technique

While the phenomenon now known as the Purkinje shift had been described long before Frank Tenney Johnson’s career, I have found no documentary evidence that Johnson knew it by name or approached his nocturnes through a formal theory of visual physiology. The Czech physiologist and polymath Jan Evangelista Purkyně described the effect in his 1819 doctoral work and elaborated on it in later publications. The term “Purkinje phenomenon” was proposed in 1882. What is documented, however, is that Johnson consciously studied how color changed under reduced illumination, repeatedly observing and experimenting with the changing appearance of colors in moonlight.

As early as 1904, Johnson wrote to his wife from Colorado about watching daylight fade and the moon rise, describing the experience as an opportunity to study how “the different colors change under the moonlight.” Melissa J. Webster, who has written extensively on Johnson’s nocturnes, identifies this as an early indication of an interest that would continue throughout his career. In 1931, Johnson described moonlight as “nature’s indirect lighting,” emphasizing that in the clear air of the West it could still reveal the structure of rocks and considerable color in the foreground.

His biographer Harold McCracken likewise records that Johnson spent considerable time studying and experimenting to simulate daylight colors under moonlight and starlight, even developing a special preparation for the white underpainting used beneath his nocturnes. Whatever Johnson knew or did not know about the physiology of night vision, the historical record is clear on one point: he was actively observing the changing relationships of color, value, and visibility as illumination fell. That makes the Purkinje shift useful not as a claim of scientific influence, but as a modern way of understanding some of the visual relationships Johnson discovered through observation. As light levels fall, the eye does not treat all colors equally. Long-wavelength reds and oranges tend to lose apparent brightness relative to shorter blue-green wavelengths. At the same time, high-reflectance surfaces can remain conspicuous even as much of the surrounding scene collapses into darkness. Johnson’s nocturnes repeatedly organize the painted world in comparable terms.

The effect is especially clear in Moonlight in the Canyon (1928). While the painting indeed contains a notably warm range of ochres, muted reds, browns, and flesh tones, the scene’s broad structure is established by a much cooler range in the blue sky, blue-green canyon shadows, and cool notes distributed through the foreground. Against these fields, the pale foreground horse and the rider’s light shirt become exceptionally conspicuous. These surfaces, which might appear as brilliant whites or near-whites in daylight, are notably subdued and appropriately chromatic for their position within the painting’s value structure. Surrounded by darker canyon walls, darker clothing, and darker horses, they remain strikingly bright when much else recedes. The second rider, by contrast, is absorbed much more deeply into the shadowed canyon. Even the small red accents of tack and clothing remain visible without becoming major sources of brightness.

This is precisely why the Purkinje shift should not be understood as a blue-green veil laid over the world. Johnson still retained warm color where the scene required it. The illuminated canyon wall on the right contains substantial ochre and earth color, while the foreground horse itself contains warm cream and brown passages. What changes is the hierarchy. Cool color carries much of the nocturnal atmosphere while warmer locals remain restrained, not holding the visual prominence they might possess in full daylight.

The Pony Express (1924) makes this hierarchy even easier to see. Much of the landscape and sky is organized in deep blue-green and turquoise-green passages. Against them, the pale horse at the left becomes one of the most immediately visible forms in the painting, while the brown horses, riders, saddles, and adobe architecture sink more readily into the surrounding darkness. At the same time, Johnson introduces a concentrated area of orange-yellow light at the doorway behind the riders. This warm light matters because it prevents us from reducing his technique to a simplistic recipe in which “warm equals dark” and “cool equals light.” A sufficiently strong local light source can of course remain bright at night. Johnson permits that warmth to flare appropriately, but confines it to a small area. The dominant visual field remains cool and low-keyed.

Girl and Cowboy (1914) offers yet another variation on the same problem. Here again, Johnson allows substantial warmth into a nocturnal composition while maintaining a strong alignment with the biases of the Purkinje shift. The face of the traincar at the left contains deep ochres, browns, and muted orange, while smaller warm notes appear in the horse’s tack and the figures themselves. Yet these passages are held within comparatively subdued values. The painting is particularly useful because it demonstrates how varied and flexible Johnson’s moonlight technique was. Warm and cool colors coexist, but as with the Purkinje shift, they do not carry equal visual weight.

Across these works, a consistent pattern emerges. Blue-green and cool passages frequently carry the broad structure of the nocturnal scene. Pale horses, clothing, and rock surfaces remain conspicuous against surrounding darkness. Browns, reds, and earth colors survive, even sometimes quite strongly, but their brightness and extent are carefully negotiated. The range of color narrows without collapsing into the near-monochrome we might associate with very low-light conditions. Interestingly, Johnson’s own description of moonlight emphasized that night could still reveal both structure and color, and he demonstrated this in his brilliant paintings. Darkness did not erase color from his world; it simply changed its power structure.

More Than the Palette

The Purkinje shift may help to explain an important part of Johnson’s nocturnal palette: why cool blue-green passages can retain so much visual presence while reds, oranges, and earth colors tend to fall back into darker, more subdued color. But color alone does not create the illusion of night that Johnson achieved. His nocturnes also depend, often just as strongly, on a broader configuration of detail, contrast, edges, and value.

One of the most obvious changes is the suppression of unnecessary detail. In low light, the eye does not resolve the world with the same precision available in daylight, and Johnson does not attempt to describe every surface equally. Large areas of clothing, landscape, architecture, and shadow are simplified into broader masses. Details are concentrated where they are needed to communicate certain aspects of the subject and, when appropriate, allowed to disappear elsewhere.

The shadows are similarly compressed. Rather than filling dark passages with numerous finely separated values, Johnson often allows neighboring dark forms to merge into simplified regions. A rider may partially disappear into a horse; a horse may merge into the ground; distant rock faces may collapse into a single dark mass. The result is not an absence of structure but a more selective one. The largest value relationships remain clear even as smaller distinctions are sacrificed for the greater good.

This gives particular importance to contour and large value organization. Figures, horses, canyon walls, and buildings are often readable first as broad shapes and only second as collections of details. A pale horse against a dark landscape can be understood almost instantly, while a darker rider may be defined primarily by the contour separating him from the sky. Johnson therefore makes the scene legible with only the information necessary. In this regard, his works are a true masterclass in strategic brevity.

Highlights are also carefully rationed. A pale shirt, the face of a horse, the edge of a rock, or a small patch of artificial light can command unusual attention because there are so few competing bright notes or elements. Their effectiveness depends less on absolute brightness than on scarcity. By withholding bright, strong lights across most of the canvas, Johnson allows a handful of lighter passages to establish both illumination and visual emphasis.

Representations of depth do some of the heavy lifting for Johnson as well. As we might expect with applications of aerial or atmospheric perspective, his more pictorially distant subjects generally lose contrast, edge clarity, and chromatic distinction, allowing them to sink into the surrounding night. Foreground forms may retain somewhat stronger separations, while distant mountains, canyon walls, or buildings dissolve into broader tonal fields. This gradual loss of distinction helps create depth without requiring the extensive descriptive detail of daylight.

These devices work together. The Purkinje shift helps explain the altered color and relative-brightness relationships that Johnson observed under reduced illumination, but it cannot by itself account for the full nocturnal effect. Suppressed detail, compressed shadows, strong silhouettes, carefully rationed highlights, atmospheric recession, and selective edges all contribute to the same perceptual argument. As I hope has become increasingly clear, Johnson’s night scenes succeed not because every part of the scene has simply been darkened, but because the entire hierarchy of visual information has been changed. Color tells us that the light has changed; value, edge, contrast, and detail convince us that vision itself is operating differently.

Painting the Behavior of Vision

Frank Tenney Johnson’s nocturnes are remarkable because they solve a peculiar artistic problem. The paintings, under ordinary illumination, offer the viewer a remarkably apt experience of a moonlit night. He creates a convincing impression of a world governed by different conditions of visibility. He does this not by simply lowering every value equally, but by changing myriad relationships among things. Some colors retreat more strongly than others, pale surfaces retain unusual visual prominence, detail can disappear selectively or dramatically, shadows compress, and edges soften, merge, or sharpen according to their importance. Without a doubt, the entire visual hierarchy is altered.

The Purkinje shift helps explain one important part of this transformation: the changing relative brightness of colors as illumination falls. But Johnson’s achievement lies in translating a much broader experience of reduced light into paint. His nocturnes describe not only what horses, riders, rocks, buildings, and sky look like at night, but how differently those things become available to vision. That is why the paintings feel more convincing than scenes that merely substitute blue for daylight or blacken a familiar palette. Through sustained observation and experiment, Johnson understood that night is not simply an absence of light. It is a different ordering of what can be seen. Frank Tenney Johnson did not simply paint the colors of the night. He painted the changing behavior of vision within it—what darkness does to color, form, visibility, and ultimately the way we see.