Without an anti-reflective coating on a polycarbonate lens, what percentage of light is reflected?

• A. 10%
• B. 20%
• C. 14%
• D. 25%

Answer: (C)

Light reflects at boundaries where the optical properties change. At an air–polycarbonate surface, part of the incoming light is reflected because the refractive indices don’t match, and with two surfaces on the lens, that reflection happens on both sides. In uncoated polycarbonate lenses, the combined reflection from the front and back surfaces is commonly around fourteen percent for typical viewing conditions, which is why that option is chosen. An anti-reflective coating works by causing destructive interference of the reflected waves from both surfaces, reducing the overall reflection to only a few percent. The other numbers don’t match what’s typically seen with uncoated polycarbonate.