Updated: Jan 13
I’ve been privileged to photograph many beautiful scenes during my 25-year career as a landscape photographer, but on only a few occasions I have witnessed the extraordinarily colorful light I call gap light.
Gap light occurs when the sun finds a narrow but completely clear gap between dense clouds and the horizon right at sunrise or sunset. At its best, it can produce the most intense, saturated red light you’ll ever see in the natural world.
To understand gap light, you need to know a bit about atmospheric optics, the science of how sunlight interacts with our atmosphere. Light as it comes from the sun contains all the visible wavelengths. An astronaut flying above Earth’s atmosphere would see the light as white. When sunlight hits Earth’s atmosphere, it interacts with the molecules of oxygen and nitrogen that make up most of the atmosphere and begins to scatter. The amount of scattering depends on the wavelength. Blue light (the short wavelengths) scatters much more than red light (the long wavelengths). The result, on a clear day with the sun high in the sky, is that we see the sky as blue. Air is actually transparent, so what we’re really seeing is blue light that originates at the sun and is scattered to our eyes by air molecules.
In the middle of the day, the distance light must travel through the atmosphere before it reaches the surface of the Earth is relatively short. Enough light scatters out of the beam to make the sky blue, but the overall mixture of wavelengths is only slightly warmer in tone (more yellow) than the color of sunlight above our atmosphere, so we still see the color of the light as white.
At sunrise and sunset the light from the sun takes a much longer path through the atmosphere, as shown in figure 1. During that long journey, most of the blue light scatters out of the beam. The reddish light travels straight through, bathing clouds and high mountains with the warm glow we love to photograph.
Figure 1. At noon, when the sun is high in the sky, light from the sun takes a relatively short path through the atmosphere. At sunrise and sunset, the path is much longer.
If the sky is clear near the horizon, the light at sunrise and sunset will always be warmer in tone than the light at noon. However, during completely clear sunrises and sunsets, that vivid warm light coming directly from the sun is diluted by the bright, white light from the sky around the sun. The result is a pastel, as if you poured white paint into red paint. If, on the other hand, there is a clear gap between a dense band of clouds and the horizon, then the light can be the most colorful you will ever photograph. The dense clouds block the bright, white light from the sky surrounding the sun, and the result is a pure beam of intensely saturated light that blasts through the gap and ignites whatever it touches. Almost always, the effect is fleeting. Within a minute or two, the sun rises into the dense clouds or sets below the horizon, and the light show abruptly ends.
I’ve included two examples to make this point clear. The first shows a cascade at Columbine Falls, in Rocky Mountain National Park, during a clear sunrise. As you can see, the flowing water is picking up some muted color from the sunrise light. The second shows the same cascade when the rising sun found a narrow gap between dense clouds and the horizon. Clearly, the colorful highlights on the water are far more saturated and vibrant.
The most likely outcome on a cloudy morning is a lifeless gray sunrise that makes you wish you hadn’t gotten up at 2 a.m. and hiked for 2 ½ hours in the dark, as I did to reach Columbine Falls. If, however, the sun finds a gap between dense clouds and the horizon, the result can be an astonishing display of natural light. This maddening reality led me to coin the first of Randall’s Rules of Landscape Photography: the potential reward is always greatest when the odds against you are the longest.
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