The E-SPF Protocol
E-SPF : A relevant UV index for eyeglass lenses
Today, consumers can easily find the sun protection they need by glancing at the reference index displayed prominently on daily moisturizers, sunscreens, and sun-protective clothing. But what if consumers want a similar means to judge the protection of their eyes from the sun’s damaging ultraviolet radiation (UVR)? There has not been any global UV index for eyewear, even though there is clear evidence that UV rays can cause significant short- and long-term ocular damage.
Existing “100% UV protection” labels refers to the UV cut preventing the transmission of ultraviolet rays hitting the front side of the lens. However, up until now, even the best eyeglasses did not protect against the danger of the UV radiations coming from the back and sides of the lens (reflection). Measures have found that up to 50% of UV light reaches the eye from the rear lens surface.
“Over 90% of consumers recognized the utility of a sun protection factor for eyewear.” (1)
E-SPF, a new way to look at UV radiations Hazard and Eye Protection
Considering these measures, and in order to provide consumers and Eye-Care Professionals with the most accurate information on effective UV protection for lenses, Essilor International scientists, in conjunction with independent third-party experts, have created the Eye-Sun Protection Factor (E-SPF).
The E-SPF aims to raise consumer awareness about the importance of protecting eyes from damaging UV rays. It allows the comparison between different lenses according to their level of UV protection. Essilor International is convinced that this unique evaluation system will increase consumer knowledge on UV and help improve visual health by protecting the eye from the invisible and often irreversible dangers of UV light.
By incorporating measurements of both transmission and rear surface reflection, the E-SPF provides a simple yet effective way to grade the total protection offered by a lens. As with the index used in the skincare industry, the higher the E-SPF value, the greater the level of protection against damaging UV radiations.
“72% of consumers are unaware that clear lenses offer any protection against UV!” (1)
Essilor worked with an independent expert to develop a relevant protection index, based on a series of experimental measurements, taking into account:
- UV light passing through the lens (=Transmission) and UV reflected by the rear lens surface (=Reflection). (a)
- Corneal sensitivity to UV and solar spectral irradiance(2) as UVA and UVB do not represent the same danger for the eye. (UVB wavelenghts being more dangerous but less present in the environment, UVA wavelenghts less energetic but more present around us)
- Different positions of the sun, as in real life (in the front of the wearer as well as in the back and sides – and at different heights in the sky depending on the time of the day). (b) & (c)
- Representative frame and lens parameters (3).
Like for the international index displayed on sunscreens and skincare products, the Eye-Sun Protection Factor is a ratio between eye exposure with and without protection, that is to say with and without the lens.Direct eye exposure depends on external factors (eg, wearers morphology, frame shape, position of wear, etc…) which are not integrated into the E-SPF formula.
(a) UV captor located in the eyeball of a dummy, measuring front and back UV exposure.
(b) UV exposure measured at different positions of the sun.
(c) Actual UV exposure measured in the eyeball at different hours of the day, with sun at different height in the sky, with and without lenses. Dummy head inclined at 15°.
(1) Ipsos Omnibus survey for Essilor International – Base: 5000 respondents in 5 European countries (France, Germany, UK, Italy, Spain) 2011
Question 1: Today, sunscreen manufacturers must indicate the level of UV protection provided by their products, using an index called “Sun Protection Factor”. Would you find useful to indicate the level of UV protection for eyeglasses with clear lenses?
Question 2: According to you, can eyeglasses with clear lenses (not tinted) provide UV protection ?
(2) Short Wavelengths Technical Report International Standard ISO 8980-3
(3) Measures using average lens curvature (base 4) on a standard frame, identical for all measurements.