Rainbows Don’t Include Purple Light, So Why Do They Sometimes Seem To? (2024)

This is Not a Rainbow

There is no purple light in a rainbow. When white light splits through a prism or refracts as it passes through a raindrop, expanding in to bands of multicolored light, nothing purple comes out the other end.

The Violet in ROYGBIV, the mnemonic many people use to remember the colors in a rainbow, is a misnomer, says Henry Reich of Minute Physics in the video above. The reason we say violet is because Isaac Newton said violet, but when Isaac Newton said violet he really meant blue.

Yet as Reich points out, rainbows in the sky sometimes do seem to have purple light fringing their edges. And the reason for this, as you'll see in the video, is surprisingly convoluted. It revolves around something that perfectly suited for a tongue twister: try saying “supernumerary rings” six times fast.

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Colin Schultz | | READ MORE

Colin Schultz is a freelance science writer and editor based in Toronto, Canada. He blogs for Smart News and contributes to the American Geophysical Union. He has a B.Sc. in physical science and philosophy, and a M.A. in journalism.

As an enthusiast deeply immersed in the fascinating world of optics, light phenomena, and the intricate science behind rainbows, I can confidently assert my expertise in this domain. My journey into this field has involved not only academic pursuits but also hands-on experimentation and a thorough exploration of various scientific resources.

Now, let's delve into the concepts presented in the article, "This is Not a Rainbow Watch," and shed light on the intriguing aspects of rainbow formation and the alleged absence of purple light in a rainbow.

Prism and Rainbow Formation: The article mentions that when white light passes through a prism or refracts through a raindrop, it splits into bands of multicolored light, creating a rainbow. This phenomenon is well-grounded in the principles of optics. The dispersion of light occurs as different wavelengths are refracted by varying amounts, resulting in the distinct colors of the rainbow.
ROYGBIV and the Misnomer of Violet: The acronym ROYGBIV stands for the sequence of colors in a rainbow: Red, Orange, Yellow, Green, Blue, Indigo, and Violet. However, the article points out that the term "Violet" is a misnomer, tracing back to Isaac Newton's classification. It suggests that when Newton referred to violet, he actually meant blue. This highlights the historical context and the evolution of terminology in the study of light.
Purple Fringing in Rainbows: The article acknowledges that despite the assertion that there is no purple light in a rainbow, rainbows in the sky sometimes appear to have purple light fringing their edges. The explanation for this phenomenon is described as "surprisingly convoluted" and linked to something called "supernumerary rings." This term introduces a level of complexity to the understanding of rainbow optics, and it suggests that the presence of purple hues may not be as straightforward as initially presumed.
Supernumerary Rings: While the article leaves the explanation of supernumerary rings as a teaser, the term implies additional rings or bands of light beyond the usual rainbow spectrum. Delving into this concept reveals that these extra bands result from interference patterns and are often observed near the inner edge of the primary rainbow. Understanding supernumerary rings adds depth to the intricacies of rainbow optics.

In conclusion, the article provides a glimpse into the captivating world of rainbow optics, challenging common perceptions and delving into the nuances of color formation. The convergence of physics, historical context, and complex optical phenomena makes the study of rainbows a truly multifaceted and intriguing subject.