|Sunrise aspen, Rocky Mountain National Park, Colorado|
For 18 years now, I've been specializing in wilderness landscape photography. During that time, I've been privileged to photograph many beautiful scenes, but on only a dozen occasions have I witnessed the rarest light of all. In my experience, truly extraordinary light occurs in two ways. In the first, the sun finds a narrow gap between dense clouds and the horizon precisely at the moment of sunrise or sunset. For just a minute, maybe only seconds, a beam of saturated light blasts through the gap and ignites the subject with the most colorful natural light you'll ever see. In the second situation, the sun, while still below the horizon, paints a broad bank of clouds with richly colored light. These clouds, which can be inside the frame or out, now become the dominant light source. While glowing clouds are beautiful, of course, it's the light those clouds bounce onto the landscape below that's truly remarkable. Like a giant softbox in the sky, the colorful clouds illuminate the landscape with a warm, soft, yet still directional light. The photograph seems to be suffused with an ethereal glow.
A weathered juniper and the Green River Overlook glow pink at dawn, Canyonlands National Park, Utah.
Light And The Atmosphere
To understand how these two situations produce such unusual light, it helps to know a little bit about atmospheric optics, the science of how sunlight interacts with our atmosphere.
The sun emits light at all wavelengths, which means all colors. When sunlight strikes our atmosphere, however, it begins to interact with air molecules in a process called Rayleigh scattering. Blue light scatters much more strongly than red light, which is why the sky is blue on a clear day.
The amount of scattering is dependent on the distance the light travels through the atmosphere. At noon, the path length through the troposphere (the dense layer next to the Earth) is relatively short, roughly 11 miles or so. Enough blue light scatters out of the beam to make the sky blue, but the remaining light is still a mixture of wavelengths that we perceive as white. At sunrise and sunset, however, sunlight takes a much longer path through the troposphere because the light is traveling obliquely through the atmosphere, along a tangent to Earth's surface, rather than along a path perpendicular to Earth's surface. For example, if you're photographing an old barn in Kansas at sunrise, the path length through the troposphere is roughly 235 miles. At sunrise or sunset on a clear day, most of the blue light scatters out of the beam. The reddish light passes straight through, giving you warm light on your subject.
Windom Peak, Sunlight Spire and Sunlight Peak from South Sunlight Lake at sunrise, Weminuche Wilderness, Colorado.
Now let's say you're photographing wind-sculpted snow on the summit of 14,259-foot Longs Peak in Colorado, which rises abruptly above the plains 9,000 feet below. The path length through the atmosphere will be even longer because the sun has to enter the atmosphere, skim Earth's surface somewhere near that Kansas barn, then continue through the atmosphere to the summit of Longs Peak, a total of roughly 360 miles.
The exact numbers aren't important, but the principle is: Tall mountains that tower over nearby plains can get amazing light, particularly if the sun finds a narrow gap between dense clouds and the horizon.
The most vivid red light I've ever seen has occurred in exactly that situation, but "gap" photos aren't confined to the mountains. To understand gap photos, in general, let's first consider what happens during a cloudless sunrise. When the sky is clear, the colorful light coming directly from the rising sun is diluted by the bright, white light from the sky around the sun. It's like pouring white paint into red paint—the result is usually a pastel color that's pleasing, but not extraordinary. If the sun finds a gap between dense clouds and the horizon, however, the clouds block that bright, white light from the sky around the sun, and the result is some of the most spectacular light you'll ever see.
Mount Sneffels at sunset, Mount Sneffels Wilderness, Colorado.
If the sun is in the frame, it also can be some of the most contrasty light you'll ever see, which poses an exposure challenge. Often, a three-stop, hard-edged grad neutral-density filter will do the trick. If you don't have one handy, bracket widely. You'll then have the option of creating a virtual split ND by combining two frames, one exposed for sky and one exposed for land, using a gradient drawn on a layer mask to merge the two frames. [See Glenn Randall's article "The Rembrandt Solution" in the September 2009 issue of OP or on the OP website for full details on this procedure.] You also can use an HDR software package such as Photomatix (www.hdrsoft.com) or HDR Efex Pro (www.niksoftware.com) to hold good detail throughout the frame.
Now let's take a look at the atmospheric optics of "glow" photos, where a large bank of clouds lights up with such strong and colorful light that the clouds themselves become the dominant light source. First, consider what happens on a completely clear morning. When the sun is below the horizon, the blue sky is actually the dominant light source. Photographs taken under this lighting usually have inadequate contrast and a somber, cool cast. Photographs taken precisely at the moment of sunrise have a warm tone, with moderate contrast, but within a few minutes the contrast has strengthened dramatically, often too much so, and the light is basically white.
Glow photos, on the other hand, are warm in tone with soft, but not flat contrast. The part of our visual system that sees depth and dimension is color-blind. It works strictly on luminance values, or differences in brightness. In effect, it's a black-and-white system, which is why shadows are your friends, giving your images dimension and depth, and why both frontlit photos and those taken before sunrise and after sunset on clear days (when the lighting is all shadow) can appear flat. Glow photos hit the perfect balance—enough contrast in the land to reveal form, but not so much contrast that your sensor has trouble straddling the difference in light intensities between highlights and shadows.
Exposure for the land portion of glow photos is easy, since the lighting is soft. The sky can be very bright, however, particularly if the glowing clouds are in the frame. One solution is to spot-meter the sky, then place the brightest part of the sky as high in the tonal scale as you can without clipping the highlights.
Where To Find Gap And Glow Light
Glow photos can occur almost anywhere. I've even seen a perceptible mauve glow in the depths of Colorado's aptly named Black Canyon of the Gunnison. All that's required is a sufficiently large bank of clouds that light up brightly enough to overpower the light from the blue sky and shadowed blue-gray clouds, therefore becoming the dominant light source.
To take full advantage of a gap situation, you need a subject to receive the light. In the mountains, look for peaks that will receive unobstructed sunrise or sunset light, either because the peaks rise above the plains, as described earlier, or because the peaks rise at the head of valleys that face the rising or setting sun. A foreground can only receive moment-of-sunrise light if the horizon is at the same elevation or lower. The Photographer's Ephemeris (photoephemeris.com) can help you find both kinds of locations by showing you the angle of sunrise and sunset at different times of year, as well as the elevations of obstacles that can block sunrise or sunset light.
When To Find Gap And Glow Light
Finding both gap and glow photos is a matter of luck, but there are ways to improve your odds. The first is to arrive early and stay late. The best glows often peak 15 to 30 minutes before sunrise or after sunset, then fade. I try to arrive at my shooting location 45 minutes to an hour before sunrise so I have time to dress warmly and set up. There's very little time between the beginning of civil twilight, when it becomes light enough to see without a headlamp, and the moment of peak light, so it's important to scout the location the day before, when you have ample time to find the perfect foreground and dial in the best possible composition.
A second way to improve your odds is persistence. Both kinds of photos depend on the presence of clouds, of course. It's one of the paradoxes of landscape photography that widespread clouds increase the risk of getting skunked and increase the chances of getting a very good photo, if you get one at all. It's awfully tempting to poke your head out of your tent or bedroom window, see clouds blotting out the stars and go back to sleep. Don't succumb. Sooner or later, you'll miss a great shot. Whenever I get tempted to hit the snooze button (which is almost every time I shoot), I remind myself of the first rule for chasing great light—the potential reward is always greatest when the odds against you are the longest.
You can see more of Glenn Randall's work, sign up for his monthly newsletter, read his blog and learn about upcoming workshops at www.glennrandall.com.