Light and color
Sunlight reaches Earth in energy waves of varying length. The total of sunlight’s visible wavelengths combine give us light that appears white. The colors we perceive when specific wavelengths within the visible spectrum are absorbed or scattered, with each wavelength creating a distinct color. While the visible portion of the sun’s energy generates a virtually infinite number of colors, we’ve all become familiar with the arbitrary color name labels assigned to wavelength points throughout the spectrum.
Moving from the longest visible wavelength to the shortest, visible light breaks down into some shade of red, orange, yellow, green, blue, indigo, or violet. Not coincidentally, these are also the colors of the rainbow we see when the white light of the sun, separated by refraction in airborne water droplets, is reflected back to our eyes. Maybe you remember from your college physics days the mnemonic acronym for the rainbow colors and their order (from the outermost to the innermost color): ROY G BIV.
When a beam of sunlight passes through a vacuum (such as space), all of its wavelengths reach our eyes simultaneously and we perceive the visible portion as white. When sunlight encounters something (like a tree, a rock, air molecules, or whatever), some of its light will either be absorbed or scattered, depending on the wavelength and the properties of the interfering medium. So, unless we’re in space, the light that eventually reaches our eyes has either been reflected or stripped of certain wavelengths by whatever it encountered on its journey.
For example, a patch of fresh snow reflects all of the sun’s visible wavelengths uniformly and appears white to our eyes. A piece of coal uniformly absorbs most of the sunlight that strikes it, so we see coal as black. And when sunlight strikes a leaf, all of its wavelengths except those that we perceive as green are absorbed, while the green wavelengths bounce to our eyes.
Color in the sky
Since our atmosphere is not a vacuum, sunlight is changed simply by passing through the air. In an atmosphere without impurities (like dust, smoke, and water vapor), light interacts only with air molecules. In very simple terms, an air molecule will scatter any wavelength that’s smaller than it is, so the shortest wavelengths are most easily scattered. This scattering of incoming solar energy by atmospheric molecules becomes a filter that catches the violet and blue wavelengths first, allowing the longer wavelengths to pass through and continue their journey to more distant eyes.
When the sun is overhead, sunlight travels through a relatively small amount of atmosphere. The wavelengths that reach our eyes are the first to be scattered, the short violet and blue wavelengths, making the sky blue (the sky appears more blue than violet because our eyes are more sensitive to blue light).
On the other hand, when the sun is on the horizon, the light that reaches our eyes has passed through much more atmosphere than it did when the sun was directly overhead. The shorter violet and blue wavelengths are long gone, bluing-up the sky for others on their way, and the only remaining wavelengths are the longer, less easily scattered, orange and red wavelengths. It’s sunset! (Or sunrise.)
Airborne impurities dampen the atmosphere’s filtering process, so contrary to popular belief, a vivid sunset requires clean, unpolluted air. That’s because smoke, dust, and water molecules are much larger than air molecules. Rather than only scattering specific colors the way tiny air molecules do, larger molecules scatter much more completely—in other words, instead of scattering only the blue and violet wavelengths, polluted air catches lots of orange and red too (and everything in between).
Anyone who has blended a smoothie consisting of a variety of brightly colored ingredients (such as strawberries, blueberries, cantaloupe, and kale—uh, yum?) knows the smoothie’s color won’t be nearly as vivid as any of its ingredients, not even close. Instead you’ll end up with a brownish or grayish muck that at best might be slightly tinted with the color of the predominant ingredient.
Verify this yourself: The next time a storm clears, check the color in the sky—whether it’s midday blue, or sunset red, it’s easy to see how much more vivid the color is when the air is clean. And what’s better known for its sunsets, Hawaii, where it rains almost daily, or Los Angeles, with its urban sprawl and exhaust-spewing vehicles?
Another source of color at sunset has become all too familiar to anyone in or near wildfire-prone regions is red-rubber-ball sunsets when a fire is nearby. A vivid sunset requires intense sunlight, the more intense the better. In a typical brilliant sunset, while the rest of the sky is filled with color, the sun itself is far too bright to photograph as anything but a white disk (without rendering the rest of the scene much too dark). But when sunlight has to battle its way through smoke particles, the total amount of light is significantly reduced and there’s not enough scattered light of any wavelength to color the sky. But look straight at the sun—it’s so inherently bright that some of its longest wavelengths have battled their way to your retinas, turning the sun red while the rest of the sky is a murky brownish-gray.
Getting the most from your sunset images
Any time rain has cleared the atmosphere and the remaining clouds are mixed with sunlight, there’s a good chance for a vivid sunrise or sunset. I have a few go-to locations near home, and at my frequently visited photo locations (Yosemite, Grand Canyon, Death Valley, Hawaii, and so on) that I beeline to when the conditions for color in the sky look promising.
Wherever I am, as I prepare my shot shortly before the sunset show begins, I look for clouds receiving direct sunlight. This is the light that will most likely color-up at sunset, starting with an amber glow that transitions to pink, and red. Conversely, if no clouds are getting light shortly before sunset, that may be an indication that the sunset will fizzle. But don’t give up, because Nature is full of surprises.
A couple of mistakes inexperienced photographers often make is giving up on sunset too soon, and forgetting to check the sky behind them. Some of the best sunsets I’ve ever seen have happened when the sun slipped through an unseen hole in the clouds just below the horizon. And shortly after the sun sets, the pink vestiges of the longest wavelengths still color the eastern horizon. As this color deepens, the steely blue of the Earth’s shadow starts to descend. This combination of rich color and soft, shadowless light creates some of the best color and light for photography. Even when the scene appears too dark to your eye, don’t forget that your camera can accumulate light and bring out color and detail lost to your eye.
Maximizing color in the high dynamic range conditions of a sunset requires careful exposure. Rather than trusting the preview image on your scenes with extreme contrast, it’s essential to trust your histogram. If the histogram for a high dynamic range sunset scene looks good (highlights and shadows not clipped), it’s likely that on the LCD the highlights will look too bright, and the shadows too dark. Resist the urge to fix one or the other in the field, and instead trust that you’ll be able to recover both in processing later. If you’re not sure (or just don’t trust your ability to read the histogram), backet your exposures by a stop or two around what you think is best.
And don’t forget to check your RGB histogram—even if the luminosity histogram looks good, it’s possible that the red channel is clipped and you’ll need to reduce your exposure a little.
You can read more about metering in my Manual Exposure article.
For example: Sentinel Dome, Yosemite
Sentinel Dome in Yosemite provides a 360 degree view of Yosemite and surrounding Sierra peaks. Among the many reasons it’s such a great sunset spot is that from atop Sentinel Dome you can see what’s happening on the western horizon and plan your shoot long before sunset arrives. On this summer evening I was up there shortly after an afternoon rain shower. Though air was crystal clear, lots of clouds remained—and there was an opening on the western horizon for the sun to slip through just before disappearing for the night.
Rather than settle for a more standard Half Dome composition, I wandered around a bit in search of an interesting foreground. I ended up targeting this group of dead pines on Sentinel’s northeast slope, a couple of hundred feet down from the summit. It was no coincidence that sunset that night, one of the most vivid I’ve ever seen, came shortly after a storm had cleansed the atmosphere. Not only did the clouds fire up, the color was so intense that its reflection colored the granite, trees, and pretty much every other exposed surface.
For example: Hilltop Oaks, Sierra Foothills
I was driving the Sierra foothills east of Sacramento looking for the right subject to put with this fiery sunset. Earlier in the sunset it had simply been a been a matter of finding a photogenic tree (or trees), but with the sun more than 15 minutes below the horizon, the foreground was so dark I needed a subject to silhouette against the sky—anything else would have been lost in the rapidly blackening shadows. These trees showed up just in the nick of time.
Color like this comes late (or, at sunrise, early), in the direction of the sun long after most people have gone to dinner (or while they’re still in bed). Everything in this scene that’s not sky is black, which is why my subject needed to stand out against the sky. I was so happy with my discovery that these trees have become go-to subjects for me—browse my galleries and count how many times you see one or both of them (often with a crescent moon).
For example: South Tufa, Mono Lake
The air on Sierra’s east side is much cleaner than air on the more populated west side, and the clouds formed as the prevailing westerly wind descends the Sierra’s precipitous east side are both unique and dramatic. Mono Lake makes a particularly nice subject for the Eastern Sierra’s brilliant sunrise/sunset shows. Not only does it benefit from the clean air and photogenic clouds, Mono Lake’s tufa formations and often glassy surface make a wonderful foreground. The openness of the terrain surrounding Mono Lake allows you to watch the entire sunrise or sunset unfold. Many times over the course of a sunrise or sunset I’ve photographed in every direction.
The image here was captured at the start of a particularly vivid sunrise. The air was clean, with just the right mix of clouds and clear sky; perfectly calm air allowed the lake’s surface to smooth to glass. I find that the more I can anticipate skies like this, the better prepared I am when something spectacular happens. In this case I was at the lake well before the color started, but because it looked like all the sunrise stars were aligning, I was able to plan my composition and settings well before the color started.