The Phenomena of Light and Color

The Golden Wall, 1961
Hans Hofmann (American, 1880–1966)
60 x 70 1/4 in.
Oil on canvas
Mr. and Mrs. Frank G. Logan Purchase Prize Fund, 1962.775

The Chemistry and Physics of Light and Color

The Phenomena of Light and Color
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To paint well is simply this: to put the right color in the right place.
— Paul Klee

A recent survey on National Public Radio asked people what they consider to be the "opposite" of science. The majority of respondents named the arts and humanities. While this may be common opinion, this course seeks to demonstrate that art is precisely not the opposite of science. These two disciplines are inextricably linked, in part, by their common interest in understanding and exploiting the phenomena of light and color.

What Is color?
To understand color, it is first necessary to understand light. Light is usually defined as that portion of the electromagnetic spectrum visible to the average human eye. It is commonly called “visible light” and subdivided into seven major colors—red, orange, yellow, green, blue, indigo, and violet. Visible light lies on the electromagnetic spectrum in between infrared and ultraviolet light.

Color may be defined both in objective terms, as specific electromagnetic frequencies in the visible-light range, and in subjective terms, as something perceived and experienced by an individual. The objective components of color are: a source of radiant energy, like the sun or a light bulb; a medium through which that energy travels, such as air; and an object, such as an apple, that absorbs and reflects different portions of the light spectrum. The subjective components of color are: the apparatus that responds to the reflected light—the cones and rods in the retina of the eye—and the brain that interprets the information received as color and generates sensations in response to that information. The optic nerve carries visual information from the cones and rods to the visual cortex of the brain, where the experience of color is made conscious and human emotions, associations, and memory are generated.

Terms to help describe a specific shade of a color are:

hue—the local color of an object, identified by a common name such as red, orange, yellow, green, blue, indigo, or violet. Hue is determined by the wavelengths of light that are reflected and absorbed by the object.
value—the degree of lightness or darkness of a hue, such as pastel pink or gem-tone red
saturation, or chroma—the relative intensity of a hue when compared to gray
temperature—the relative warmth or coolness of a color. Blues, greens, and purples, or colors containing blue, green, or purple undertones are cool colors. Reds, oranges, and yellows, or colors containing red, orange, or yellow undertones are warm colors.

Is Color Relative?
The perception and effects of colors depend on their context. This is why a particular red may appear much redder when adjacent to green than when surrounded by a gray background—the surrounding green or gray changes how that red is perceived. The artist Joseph Albers (1890–91), experimented with this phenomenon in his abstract, geometric collages. In one exercise, Albers cut four identical gray squares from the same piece of paper and placed them on four different-colored backgrounds. When mounted on their own individual backgrounds, the gray squares looked entirely dissimilar. Despite our knowledge that the grays are “the same” we cannot force our brains to see them that way. In another exercise, Albers chose different shades of the same color and tried to make them look identical in hue, value, saturation, and temperature by placing them each on different backgrounds (try this online). While the colors in both exercises may appear to change in relationship to each other, their tonal and value relationships to their background is the same whether viewed under full spectrum, neon, or florescent light. This effect is called color constancy.

Albers also experimented with afterimages, a phenomenon we all experience but typically do not notice. The clearest way to consciously experience an afterimage is to stare at a single solid color, such as a big red dot, for a minute and then quickly shift your gaze to a white wall. Most people report that, while staring at the red dot, a momentary “aura” of the color’s complement—in this case, green—hovers around the initial color and intensifies momentarily when the first color is removed. This phenomenon has been noted for centuries and occasionally exploited by artists. The 15th-century Northern Renaissance painter Mattis Grünewald (c. 1470–1528) used the effect in his famous Isenheim Altarpiece (c. 1515), an altarpiece commissioned by a hospital to help treat horrible and rampant skin diseases. In the color-saturated central Resurrection panel, the brilliant yellow, orange, and red sun is ringed by an aura of green—red’s complement—which makes the orb vibrate against the dark night sky. The 19th-century Impressionist artist Claude Monet (1840–1926) also made use of this phenomenon in his stacks of wheat series (1890–91). Nearly all of his wheat stacks are rimmed with auras of complementary colors, which lends them a kind of hazy, spectral glow. Monet claimed to see afterimages and held that, if he saw them, he ought to paint them. As artists have used this effect to create beautiful visual results in their paintings, scientists studied afterimages. Their investigations of the phenomenon are revealing evidence about the way the retina and visual cortex function.

Illusions of Space and Movement
Artists have also explored spatial relationships generated by color contrasts. In general, warm colors—reds, oranges, yellows—typically advance in the picture plane, while cool colors—blues, violets, some greens—recede. The Renaissance artist Leonardo da Vinci (1452–1519) used this illusion to create the effect of atmospheric perspective in his famous Mona Lisa (1503–06). In this painting, the woman’s figure is composed primarily of warm hues, while the landscape in the background is composed primarily of cooler blues and greens. This distinction in color temperature serves to place the figure in advance of the background. The 20th-century artist Hans Hofmann was also interested in color-generated spatial relationships, although he was mainly concerned with subverting this impression that cool colors recede and warm colors advance. In The Golden Wall (1961) (above), Hofmann explored a sensation he called “push-pull.” By overlapping carefully chosen fields of color, the artist forced the colors to move forward and backward in unexpected ways, giving the unnerving feeling that the canvas pulsates in three dimensions. Contrary to expectation, the blue area in the upper-right corner of this work “pulls” forward, while the red-orange areas around it “push” backward.

Activity: The Relativity of Color

  • Colored paper—preferably many colors, some very close in hue and/or value
  • Glue
  • Scissors

Choose one color and cut four identically sized squares. Then choose four different colors and cut four larger identically sized squares. Paste the small squares onto the larger squares and note how their hue changed in relationship to the background. Use the vocabulary above to describe each small square.

Now choose two different colors that are similar in hue and value and cut one small square of each. Search through the choices of colors to find two background colors that, when the smaller squares are placed on them, make the small squares appear similar in hue and value. Experiment until you find the combination of colors that makes the small squares appear exactly the same.

Finally, find three pieces of paper of different color that, when placed next to each other, appear as though they are overlapping. The trick here is for the third color to appear to be the combination of the first two hues and slightly lower in value and saturation.

Find out more about pigments, mediums, and the paints they create at http://webexhibits.org/pigments/index.html.

Adapted from the lecture “The Physics and Chemistry of Light and Color” by Daniel Barber. http://www.daniel-barber.com