How to Create Rainbow Effects with Primary Colors

By Valerie Njee

Rainbow effects in the atmosphere are created when sunlight interacts with water droplets or ice crystals through refraction, reflection, and diffraction. Common phenomena include rainbow arcs, iridescent clouds, and sun dogs, requiring the sun to be behind the observer at a low angle.

Key Atmospheric Rainbow Phenomena

  • Rainbows: Formed when sunlight refracts (bends) as it enters raindrops, reflects off the back, and refracts again upon exiting, separating into spectral colors.
  • Cloud Iridescence: Produces pastel, rainbow-like colors within clouds. It is caused by diffraction, where tiny water droplets or ice crystals scatter sunlight, often appearing in altocumulus or lenticular clouds.
  • Sun Dogs (Parhelia): Colored, bright spots that appear 22 degrees to the left or right of the sun, formed by sunlight refracting through plate-shaped ice crystals.
  • Circumhorizontal Arcs: Also known as “fire rainbows,” these are large, colorful bands that appear parallel to the horizon, caused by sunlight refracting through high-altitude ice crystals. 

Optimal Conditions

  • Position: The sun must be behind the observer and below 42° above the horizon.
  • Components: Sunlight, suspended water droplets (rain, mist, or spray), and clear air in the direction of the sun.
  • Best Time: Early morning or late afternoon.
  • Locations: Often seen near waterfalls, in mist, or in high-altitude clouds (cirrostratus/cumulonimbus)

Artificial Atmosphere Rainbows
You can replicate these effects by mimicking the necessary conditions: 

  • Sprinkler Method: Spray a fine mist of water from a hose on a sunny day with your back to the sun.
  • Prism Method: Pass sunlight through a glass prism to refract and disperse light into its color spectrum.
  • Water/Mirror Method: Place a mirror in a bowl of water, directing sunlight to reflect onto a light-colored surface.

Here are Different Ways Rainbow Effects Are Created

Rainbows and rainbow‑like phenomena can form through light interacting with water droplets, ice crystals, or particles in the atmosphere. Each effect has its own mechanism and visual signature.

Primary Rainbow (Atmospheric)

Created when sunlight enters a raindrop, bends (refraction), reflects inside the drop, and exits.

  • Produces the classic arc with red on the outside, violet on the inside.

Secondary Rainbow

Formed by two internal reflections inside raindrops.

  • Appears fainter and reversed: red inside, violet outside.

Halos

Caused by sunlight passing through ice crystals in cirrus clouds.

  • Often appear as rings around the sun or moon.

Sundogs (Parhelia)

Bright rainbow‑colored spots on either side of the sun.

  • Formed by ice crystals acting like tiny prisms.

Fogbows

Similar to rainbows but formed in fog droplets, which are much smaller.

  • Appear white or faintly colored.

Glory

A circular rainbow seen around the shadow of an observer (often from airplanes).

  • Caused by diffraction of light around tiny droplets.

Iridescent Clouds

Pastel rainbow colors appearing on thin clouds.

  • Created by diffraction when sunlight interacts with tiny, uniformly sized droplets.

Circumhorizontal Arc (“Fire Rainbow”)

A wide, horizontal band of rainbow colors.

  • Formed when sunlight passes through plate‑shaped ice crystals at a specific angle.

Creating Rainbow Effects Using Primary Colors

You can also create rainbow‑like visuals using primary colors (red, blue, yellow in art; red, green, blue in light).

1. Color Mixing (Additive – Light)

Using RGB light sources, you can create rainbow gradients by blending:

  • Red
  • Green
  • Blue

Digital screens use this method to simulate rainbow effects.

2. Color Mixing (Subtractive – Pigments)

Using RYB pigments, artists create rainbow effects by blending:

  • Red
  • Yellow
  • Blue

This produces a painted or printed rainbow spectrum.

3. Diffraction on Surfaces

CDs, DVDs, soap bubbles, and oil films create rainbow patterns because:

  • Light hits microscopic grooves or thin layers
  • Colors separate due to interference and diffraction

This is a physical rainbow effect, not color mixing.

4. Prism or Glass Refraction

A simple glass prism can split white light into a full spectrum.

  • This is the same physics as atmospheric rainbows.

5. Water Spray + Sunlight

Spraying water from a hose in sunlight creates a miniature rainbow.

  • Works because droplets act like tiny prisms.