Blue light and ultraviolet radiation can cause acute eye hazards. Further, increasing evidence suggests that blue light contributes to chronic diseases, such as cataracts and age-related macular degeneration. The use of optical radiation protective devices, such as goggles, is a simple means to avoid eye damage when working with high-irradiance sources. For the eye protection to be optimal, it must sufficiently reduce the spectral irradiance at the relevant wavelengths.
An investigation of eye protection filter devices intended for light curing of dental materials performed a decade ago showed that only half of the filters protected adequately when the exposure (source irradiance, radiance and time) was taken into account. We will report a recent follow-up including 13 eye protection filters available on the Scandinavian market. In addition to the risk assessment method used in the first investigation (high safety margin), based on the maximum filter transmittance, another method was used which was based on the overlap between source spectral emissions and the filter spectral transmittance (low safety margin).
Spectral characterisation of nine sources (dental curing LED lamps) was undertaken using a double monochromator spectroradiometer (model DTM300, Bentham Instruments Ltd, Reading, UK). An optical light guide, fitted with a 100 mm diameter integrating sphere, optionally a 10 mm diameter cosine-corrected flat diffuser served as input optics for measurements of spectral flux and irradiance. Wavelength and irradiance calibrations were made according to current standards. The exitance range of the nine lamps was 635–4600 mW/cm2 (± 7%). Radiance was calculated based on planar angle measurements in the range 0.3–0.8 rad (± 21%). Spectral weighting was done as recommended by the International Commission on Non-Ionising Radiation Protection for blue light exposure to the eyes.
The resulting blue light hazard weighted radiance range was 424–3148 mW/cm2sr (± 28%). The filter transmittance values obtained varied by a factor 105. The “maximum permissible exposure time” (tmax) for the protection filters were calculated with high and low safety margins and for direct and reflected light. According to the high safety margin estimations, 54% of the filter products had acceptable transmittance while low safety margin estimations increased the percentage to 77%. Acceptable tmax values, i.e. full work-day protection (worst-case estimate), corresponded to a transmittance percentage of 0.1% in the wavelength range 390–525 nm.