The technical specifications of sunglasses primarily measure their protective and optical performance. The most fundamental metric is the level of ultraviolet (UV) protection-often labeled as "UV400" or "100% UV protection"-which indicates that the lenses block UV rays with wavelengths up to 400 nanometers; this is a crucial indicator of protective capability.
Another key parameter is Visible Light Transmission (VLT), which refers to the percentage of light that passes through the lenses. Lower transmission rates mean darker lenses and stronger light-blocking capabilities. The industry typically categorizes lenses into five classes (0 through 4): Class 0 offers the highest light transmission, making it suitable for low-light conditions; Class 1 is suited for overcast days; Class 2 is ideal for everyday urban use; Class 3 is designed for bright outdoor environments; and Class 4 is intended for extremely bright conditions but is generally not recommended for driving. Additional functional specifications include polarization, lens material (such as polycarbonate, resin, or glass), impact resistance, and coating types (anti-reflective, anti-scratch, or oleophobic/anti-smudge). Collectively, these parameters determine the actual user experience, including visual clarity, durability, and comfort.
