What characteristic of a lens material affects its ability to bend light?

The ability of a lens material to bend light is primarily determined by its index of refraction. The index of refraction is a measure of how much light slows down as it passes through a material compared to its speed in a vacuum. A higher index of refraction indicates that light will bend more when it enters or exits the lens material. This bending occurs because light changes speed as it transitions between different media with varying optical densities.

In essence, the index of refraction directly influences how effectively a lens can alter the path of light rays. This is crucial in lens design, where the desired optical properties must be balanced with material choices to achieve specific focusing characteristics.

While thickness, color, and diameter can influence other optical properties or the physical design aspects of a lens, they do not have the same direct effect on the fundamental ability of the lens material to bend light in the same way that the index of refraction does.