This is not correct. Plank and Einstein did not explain that light is both a wave and a particle. Einstein explained the photoelectric effect with the idea that light is made up of discrete packets of energy called photons, while Plank explained blackbody radiation with the idea that light is made up of waves. It was later discovered that light exhibits both wave-particle duality, which means that it behaves like both a wave and a particle depending on the experiment being conducted.