A recent study from Brazil suggests that the country’s current standards for testing the UV protection and durability of sunglasses doesn’t line up with how the lenses are actually used.
The test, which is also used in Europe, New Zealand, and Australia, is suggested to have too short a duration and too large a distance from the solar simulators to properly reflect real-world use of sunglasses.
In Brief: Sunglass Testing
The UV filters in sunglass lenses, although able to block sunlight, do degrade over time as they are subject to repeated solar irradiance. This can lead to the lenses losing their effectiveness, change the UV-protection category they fall under, and may also affect on shatterproof the lens is.
The current test standard is to expose the sun glasses to a 450W sun simulator for 50 hours straight at a distance of about 30cm. This is equivalent to about two days outdoors during the summer or four days in winter.
The Brazilian researchers wanted to see if the conditions the lenses were tested under could be reliable for determining their safety for the lifespan of the average pair of sunglasses. They found that most Brazilians replace their sunglasses every two years and wear them for roughly two hours every day. After running calculations based on the sunlight conditions in 27 Brazilian cities, it was determined that the current testing method didn’t properly account for the level of exposure the lenses would receive.
The findings state that a more appropriate test would be to place the lenses at a distance of 5cm and expose them to the solar simulator for at least 134.6 hours. The researchers emphasize that the calculations were primarily based on Brazilian cities but note that other countries, particularly those at similar latitudes, would be able to benefit from the results.
What This Means
The potential significance of these findings will obviously depend on where you live and the given UV index of your area. South American nations face stronger sunlight exposure, so eye health consequences are a larger public health concern.
Sunlight can injure the lens of the eye, cause retina damage, edema (swelling), pterygium (fleshy growth in the eye), cataracts, and cornea problems. Sunglasses with effective UV protection are the primary method of avoiding these consequences, so any possible improvements to how they are tested should be carefully evaluated.
Masili, M., et al., “Equivalence between solar irradiance and solar simulators in agng tests of sunglasses,” BioMedical Engineering OnLine, 2016; 10.1186/s12938-016-0209-7.