Wednesday, May 18, 2011

Health effects of blue light

What a difference a century makes, and 134 years even more so...

The year 1877 marked the peak of a craze to use light transmitted through blue glass to enhance crop growth and to heal animals and humans of all kinds of ills. The originator of the craze was Augustus J. Pleasonton---a Civil War general, amateur naturalist, and arguably the father of the color-healing movement that survives today. Pleasonton is featured in Chapter 11 of Paul Collins’s book, Banvard’s Folly: Thirteen Tales of Renowned Obscurity, Famous Anonymity, and Rotten Luck (New York: Picador, 2001). Collins compassionately chronicles several “brilliant but fatally flawed thinkers,” most from the late 19th century in the U.S. The frontispiece by Walt Whitman summarizes Collins’s sympathy: “Battles are lost in the same spirit in which they are won.”

Unlike some of his later imitators, Pleasonton strongly believed in his cause. His intellectual inspiration came from Robert Hunt’s 1844 Researches on Light. (No known relation to our Robert Hunt.) Pleasonton conducted several well-intentioned but ill-controlled experiments with grapevines, pigs, and even human subjects. He also published a book (on blue paper, of course) that purported some theoretical underpinnings. One passage quoted by Collins begins, “Our sun is simply a huge reflector of light,” and goes downhill from there. In 1871, after a home visit from a patent examiner and a month of waiting, Pleasonton obtained a US Patent (US 119,242). The first claim was as follows: “The method herein described for utilizing the natural light of the sun transmitted through clear glass, and the blue or electric solar rays transmitted through blue, purple, or violet-colored glass, or its equivalent, in the propagation and growth of plants and animals, substantially as herein set forth.” After a few years, Pleasonton became shocked at the quackery and nonsense whose spread he had begun, and tried but failed to enforce his patent. Modern patent attorneys would cite "laches,"* but I would make the broader attribution to the whole barn door being open…

Of course, not everyone was buying blue glass as a cure-all. Satire abounded. For example, John Carboy's book satirizing the craze gave the helpful hint: "Square pieces of blue glass weighing six pounds each may be used for dispersing a cluster of tom cats."

At the peak of the craze, the Scientific American finally cried foul and, in 1877, published many articles (sometimes more than one in the same issue) to discredit Pleasonton. The most cogent comment was that sunlight through blue glass actually contains less blue light than unfiltered sunlight, and so blue light itself could not be the agent of the observed cures.

Fast-forward 134 years. How much has changed! Patent office actions don't take just a month or two, but five years as we grow old and companies rise and fall. Not only is blue light not a healer, but it actually can cause injury to the eye’s photopigment [1]. If it betokens ultraviolet components, these components pose an injury threat to the cornea and lens of the eye [2]. In lesser doses, a blue light can also produce a dissonance between the eye’s pupillary and focus reactions, resulting in eyestrain. Blue light can also encourage wakefulness, because the eye has a special melanopsin receptor in the blue region of the spectrum [3]. This last may or may not be healthy depending on how late you stay up in front of your blue computer screen.

But one thing that hasn’t changed is the rule of logic. In view of the new knowledge, one finds that the 1877 Scientific American argument is not as effective as it first appears. Certainly absolute blue-light doses may be quantitatively associated with eye injuries, but the ergonomic problems of eyestrain and wakefulness rely more on imbalances of receptor inputs, which also manifest in---you guessed it---color perception. Accordingly, finer critical tools are needed to assess cause and effect than the notion of a “dose” of light. Besides mentioning the need for controlled experiments, I will not try to teach any of these arguments, but will defer to the work of, e.g., ISCC member George Brainard.

In any event, I recommend Collins’s book for much more than just the Pleasonton article. Try the article that gave its title to the book: Banvard’s folly, a three-mile long painting of the shore of the Mississippi River, scrolled past viewers between two rollers. It was world-famous in its own time, unknown in ours. How many of our own names or works will survive 134 years?


1. International Non-Ionizing Radiation Committee of the International Radiation Protection Association, Guidelines on limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm (incoherent optical radiation), Health Physics 87 (2), 177-186 (2004).

2. Information Page for Therapists: The Risk of Eye Damage from Bright and Blue Light Therapy and see primary research references therein.

3. S. W. Lockley, Spectral sensitivity of circadian, neuroendocrine, and neurobehavioral effects of light, J. Human-Environmental System 11, 43-49 (2008)

*Note: "Laches" means undue delay in asserting a legal right; "latches" are part of a barn door.

Michael H. Brill