Seen here are my sunglasses (top) and my regular clear glasses (bottom). In visible light (left), the sunglasses look dark and the regular glasses look clear - as expected. In ultraviolet light (right), however, both the sunglasses and clear glasses look dark.

The cause? Modern glasses commonly feature UV-filtering plastics to protect the eyes from harmful sunlight. This photograph clearly illustrates the legitimacy of this feature.

Seen here are my sunglasses (top) and my regular clear glasses (bottom). In visible light (left), the sunglasses look dark and the regular glasses look clear - as expected. In ultraviolet light (right), however, both the sunglasses and clear glasses look dark.

The cause? Modern glasses commonly feature UV-filtering plastics to protect the eyes from harmful sunlight. This photograph clearly illustrates the legitimacy of this feature.