What Is a Night Rainbow Called
A night rainbow is commonly called a moonbow or lunar rainbow. It forms when moonlight, instead of direct sunlight, is refracted and reflected inside water droplets, producing a faint, often white or pastel arc visible to the human eye. The same optical principles that create daytime rainbows apply at night, but the lower light intensity makes colors harder to distinguish without long-exposure photography or very dark skies.
Moonbows are rare because they require a bright full or nearly full moon, low ambient light, and rain or mist opposite the moon. According to NASA and atmospheric optics researchers, moonbows are most often reported at locations with persistent nighttime spray, such as large waterfalls and coastal spray zones, where droplet size and angle align with moonlight. They are not a different phenomenon from daytime rainbows; they are the same process under low-light conditions.
Where and When Moonbows Occur Most Often
Famous moonbow locations include Cumberland Falls in Kentucky, Victoria Falls on the Zambia-Zimbabwe border, and Yosemite Falls in California. These sites combine high-volume water spray with clear nighttime views of a bright moon, creating regular moonbow opportunities during full-moon periods. The U.S. National Park Service and international tourism agencies track moonbow visibility windows, typically advising that the best chances occur a few days before and after the full moon when the moon is above the horizon during evening hours.
Artificial light rainbows can form near powerful nighttime light sources that illuminate water spray or fog. Examples include illuminated fountains, mist cannons at outdoor events, and industrial spray systems. In some cases, LED and laser installations create structured rainbow-like arcs at night for entertainment and advertising. These displays rely on the same refraction and reflection physics as natural rainbows but use directed artificial light instead of moonlight or sunlight.
How Visibility and Color Differ from Daytime Rainbows
Human color vision is poor in low-light conditions because the eye shifts from cone-based photopic vision to rod-based scotopic vision, which is less sensitive to color. As a result, moonbows often appear white or faintly tinted to the naked eye, even though the same spectral separation occurs as in a daytime rainbow. Long-exposure photography reveals more color in moonbows by collecting more light over time, showing that the same red-to-violet order seen in daytime rainbows is present after dark.
For detailed atmospheric optics explanations and recent observations, refer to resources from institutions that publish peer-reviewed work on light and vision, such as the American Meteorological Society and the Optical Society. Some public datasets on atmospheric phenomena and visibility are also shared through open government science portals. For background on how human vision affects color perception in low light, see research summaries from organizations that study vision science and light measurement, such as the Illuminating Engineering Society.