'Turn on a light, or you're gonna ruin your eyes.'
Chances are some adult shouted that at you when you were growing up, or that you yourself have berated some youngster with the same advice (if the kid's actually reading, say, a book, rather than a backlit screen).
But you're probably less familiar with this version: 'Don't go to school, or you're gonna ruin your eyes.'
That is essentially what an independent UK researcher is warning.
Writing in the Royal Society for Public Health's Perspectives in Public Health, researcher Richard Hobday notes that classrooms with insufficient levels of natural light may trigger myopia in children (myopia, of course, is short-sightedness in laymen's terms, near-sightedness to our American readers).
Hobday says it's high time to re-investigate the connection, which researchers began suspecting in the mid-19th century, but which they have never conclusively proven. The theory has fallen in and out of favour over the years, with some experts claiming that genetics - not environment - cause myopia.
But with childhood myopia on the rise globally and reaching 'epidemic levels in east Asia,' Hobday calls for more studies.
'Recent research strongly suggests that the amount of light children get as they grow determines whether they will develop short sight; however, evidence that daylight in classrooms prevents myopia is lacking. Given the rapid increase in prevalence among school children worldwide, this should be investigated.'
The author says that myopia in children is 'a global public health problem,' and notes that it has been increasing for 50 years.
'The most dramatic rise has been in Hong Kong, Taiwan, Singapore, China’s cities and elsewhere in east Asia,' he says. 'In some cases, 80 per cent to 90 per cent of children leaving secondary school are short-sighted, and of these, some 10 per cent to 20 per cent have high myopia and so are at risk of blindness in later life.'
Hobday sketches out a history of how school building practices have shifted over the years, influenced by things like myopia theories, oil crises and educational theory. In one of the story's more curious factoids, Hobday notes that in the 1970s, the US state of Florida mandated that schools have no windows (and lots of air conditioning).
While no one seems yet to know for sure, it looks as though it's time to bring on more windows.
Photo is from Stocker1970 via Shutterstock