Which type of lens surface is characterized as having negative power?

A concave lens surface is characterized by having negative power. This is due to its shape, which curves inward, resembling a cave. When light rays pass through a concave lens, they diverge, meaning that they spread apart rather than converge. This diverging effect is quantified with a negative focal length, and therefore, the lens has negative optical power.

Understanding the nature of concave lenses is important, especially in optometry and optics, as they are commonly used to correct nearsightedness, also known as myopia. Myopic individuals have difficulty seeing distant objects clearly, and a concave lens helps by compensating for the eye's excessive focusing power.

In contrast, convex lenses have positive power, as they converge light rays, while plano lenses do not have any curvature and thus have a power of zero. Cylindrical lenses, on the other hand, may have either positive or negative power, depending on their orientation and design, but they are specifically designed to correct astigmatism and have a more complex surface structure.