The first blue light craze It can justifiably be said that we are living in somewhat of a ‘blue light craze’ with the benefits of lighting for health and the dangers of blue light from screens being frequently mentioned, however, perhaps surprisingly, this is not the first time we have had such a craze. After a long military career, including being promoted to Brigadier General of the Pennsylvania military in 1861, Augustus Pleasonton retired from the military after the Civil War to practice law and, in his spare time, to pursue his own private scientific experiments. Though not trained as a scientist Pleasonton developed a theory that the blue wavelengths from the sun are inherently unique and that they were especially influential in the growth of plant and animal life. He also postulated that blue light was significant in the health of humans and helped eradicate disease. He based his theory on the fact that plants flourished in the spring time and not in the winter, when the sky was less blue. Between the years 1861 and 1876, he tested this theory by growing grapes in a greenhouse-like building where he alternated direct sunlight with filtered blue light, using cobalt glass. He claimed that this method greatly increased his production of grapes. He then moved onto studies of the growth of animals e.g. pigs and cows, raised under blue light and claimed that they grew bigger. This led to a ‘blue glass craze’ with farmers and growers installing panes of blue glass. Unsurprisingly perhaps the claims about benefits of blue light also extended to treating human diseases as well. People gave enthusiastic reports about how sitting under blue glass cured diseases A woman who had been ill for a long time with some constitutional weakness was not only strengthened but absolutely cured in a short time by sitting in blue light and a man whose arm was crippled by rheumatism declared that he experienced almost immediate relief when the arm was thrust within the violet rays. And there are a number of reports of people sleeping better as a result of sitting in blue light during the day. In 1877 Pleasonton published his theory and details of his experiments in his book, entitled The Influence Of The Blue Ray Of The Sunlight And Of The Blue Colour Of The Sky and the subtitle: In developing animal and vegetable life; in arresting disease, and in restoring health in acute and chronic disorders to human and domestic animals. (Read it here here). However, although his ideas initiated the ‘blue-glass craze’, the wider world remained sceptical, in 1877 the Scientific American found it worthwhile to rebut in great detail the notion of the special virtue of blue light. After just a few years the ‘blue glass craze’ was over, although Pleasanton until he died in 1894, still insisted that he had made a valuable discovery that the world failed to appreciate. Hopefully our belief in the benefits of human centric lighting, which are for the most part still scientifically unproven, and dangers of blue light do not end up being described in the terms used by the Boston Globe when writing about Pleasonton’s ‘blue light craze’, “Indeed we hope the epidemic will be violent and proportionally short. It is amusing to see people making fools of themselves, but it soon grows wearisome.”