A prototype for measurements in visible light transmittance of sunglasses

The measurements of the transmittance of ultraviolet and infrared radiation through sunglasses are standard requirements for certification of these lenses. According to Brazilian Standard NBR15111(2004), the electromagnetic spectrum relative to UVA, UVB and UVC (100 - 400nm) and infrared (700-1400nm) must be protected, by filters, according to the lens category. The categories are in a scale of 0 to 4, according to the amount of visible light transmitted through the sunglasses. An opto-electronic set up was assembled in this work, using light sources (set of LEDs), which cover the electromagnetic spectrum in the range of 380nm - 780nm; one visible light sensor for measuring the visible light transmission through the lens of the sunglasses; and an electronic circuit to control the intensity of the LEDs light. The device performs the calibration of the light source to match the requirements by the standard. The prototype has an accuracy of 0.1% for transmission; resolution of 0.1% and correlation factor of r(2) = 0.991 for the tested lenses compared to CARY 5000 - Varian spectrophotometer.