Safety fears prompt changes to eclipse viewer specifications

17 Jun 2002

International specifications for solar eclipse viewers are to be rewritten following a three-month investigation into the safety of Mylar spectacles by Opto & Laser Europe magazine. The move is too late for the total solar eclipse across much of Europe on 11 August.

Sales of Mylar viewers from one UK manufacturer, Swan Packaging of Corby, have topped 20 million across Europe, according to managing director Bill Stillman.

The coated sheets from US manufacturer Dunmore Corporation are based on DuPont polyester film. DuPont has tried to distance itself from the controversy for some time. "None of the films manufactured by DuPont are intended to provide sufficient protection to allow them to be used for viewing the sun. Additionally, DuPont has no data to support manufacturers' claims that solar eclipse viewers using polyester film - even after the film is coated, laminated, metallized or otherwise altered - are safe for such use."

Potential dangers of viewing the sun directly with Mylar viewers were first highlighted by optics safety consultant, Roy Henderson of Bioptica, Cambridge, England. He discovered large (200 micrometres diameter) holes or voids which he claims could damage the eye. Many smaller holes of about 30 micrometres diameter occur naturally through stretching of the aluminized polyester during manufacture. These have never been considered important until Henderson pointed out that clusters of these holes may cause injury to the retina.

Ralph Chou, associate professor of optometry at the University of Waterloo, Ontario, and author of international standards for solar viewers, points out that there are two layers of Mylar in each viewer. Therefore, he claims, the chance of the holes aligning is very remote.

Now Chou has reconsidered and agreed to revise his technical standard.

"I have taken [Henderson's] suggestions regarding the presence and size limits of defects in solar viewer films seriously, and intend to incorporate them into the next revision of the technical specification," he said (Opto & Laser Europe August 1999 p9).