It is widely accepted that environmental exposure to high levels of solar UV radiation contributes to the accelerated ageing of the outer layers of the eye and skin, and the development of cataracts. Solar radiation reaching the surface of the earth ranges from ultraviolet (UV) radiation at wavelengths longer than 290 nm to radio waves in the metre range. TABLE 2 - Filter Transmittances (%) Retinal Burns Relative Safety of Solar Filter Materialsįilters intended for unaided visual observation of the sun There are now several manufacturers of solar filters intended for both visual and photographic use who were not operating in 1981 when I first published solar filter data in Sky and Telescope (August, 1981).Īn invitation to participate in a NATO-sponsored meeting on solar eclipse astronomy in June, 1996, prompted me to make spectrophotometric measurements of a variety of solar filter materials and assess whether these filters provide adequate protection for the eyes. Over the past five years, I have been asked to comment on the safety of using devices such as floppy disk media, multiple layers of space blanket (a very thin type of aluminized polyester), compact disks (CDs) and metal coated polyester wrappers as solar filters. This is especially true when the subject of protective filters for direct observation of the sun is raised. Unfortunately, despite the best intentions, the news media often provide inaccurate information on safe observing techniques.
There is a great deal of interest in watching eclipses, and in the days and weeks before an eclipse occurs, there are often news stories and announcements in the media, providing information on what will happen, and how to watch the eclipse safely. N2L 3G1 and Registrar College of Optometrists of OntarioĪ total solar eclipse is probably the most spectacular astronomical event that most people will experience in their lives. Solar Filters Time for an International StandardĪssociate Professor School of Optometry, University of Waterloo Waterloo, Ontario, Canada