To find the real value of ultraviolet glass and glass substitutes Dr. Janet Howell Clark, 39, associate professor of physiology at Johns Hopkins School of Hygiene & Public Health, measured light all last March, April and May. The discoveries, published last fortnight, were surprising:
The best ultraviolet glass, when a little old, lets only one third of the available ultraviolet sun rays pass through. (Manufacturers claim no more.)
The average amount of ultraviolet light in a 32-ft. room glazed with ultraviolet glass is only 1/600th of the noon-day’s sun.
A person in such a room absorbs as much ultraviolet rays in ten hours as he would get outdoors in one minute.
Therefore Dr. Clark decided and proclaimed last fortnight. “This amount is obviously too small to be of any great value. Any child going out for recess or any stenographer going out to lunch will get more ultraviolet radiation than she could get all day behind a window of ultraviolet transmitting glass. So, although these materials have an undoubted field of usefulness in solariums, and probably in animal houses and zoos, it is unnecessary to put them in schools and offices where it would be cheaper and more efficient to send the individuals concerned out into the sunshine for a few minutes every day at noon.”
More Must-Reads from TIME
- How the Economy is Doing in the Swing States
- Democrats Believe This Might Be An Abortion Election
- Our Guide to Voting in the 2024 Election
- Mel Robbins Will Make You Do It
- Why Vinegar Is So Good for You
- You Don’t Have to Dread the End of Daylight Saving
- The 20 Best Halloween TV Episodes of All Time
- Meet TIME's Newest Class of Next Generation Leaders
Contact us at letters@time.com