The power of a lens is its ability to bend light – the greater the power the greater the refraction of light. The +ve sign of the power indicates that the lens is a converging lens or convex lens, whereas the negative sign of the power indicates that the lens is concave or diverging lens. The S.I unit of the power is Dioptre or 1/metre. Power = 1/focal length (in m).

Power of lens is the ability of the lens to converge the rays of light falling on it. It can also be defined as P=1/f where f is the focal length. ... One Dioptre is the power of a lens whose focal length is 1 metre. Convex lens has positive power while concave lens has negative power