Abstract
Background: Many people are exposed to blue light through devices such as cellular phones, tablets and computers. Such light may affect us depending on its wavelength and blue-control lenses are now frequently used, thus influencing our daily lives. Aim: This study provides an analysis of the transmissions of blue light through 10 lenses with different blue-control coatings. Setting: The study was conducted at the Department of Optometry, University of Johannesburg, South Africa. Methods: Transmission curves of 10 lenses with different blue-control reflective coatings were compared. A control lens (the achromatic lens) was also included. The Cary Varian 5000 photo spectrophotometer from the Department of Physics at the University of Johannesburg was used to measure the spectral transmittances of these lenses with refractive indices ranging from 1.5 to 1.6. The geometric centre of each lens was aligned with the measuring axis of the spectrophotometer and spectral transmittance between 300 nm and 500 nm was measured. Results: For the 10 lenses studied, the transmission of wavelengths below 460 nm varied from 48% to 69% and for wavelengths between 460 nm and 500 nm from 33% to 55%. The differences between lenses were greater than 20%. If we changed the range of transmission to between 480 nm and 500 nm, the percentage transmitted varied from approximately 71% to 83% to give about a 12% difference between all the lenses. Conclusion: Not all lenses displayed similar transmissions of blue light and different manufacturers do not agree as to what percentage of blue light should be reflected or transmitted.