What are max Planck contribution in the field of behavior of light?

planck gave us his postulates

i.e. he said that light was quantised (comes in multiples of the smallest unit) and the energy of each quanta was E=hf (where E is energy, h is planck's constant 6.626x10^-34) and f is frequency of light wave.

this is important as Einstein expanded on this hypothesis and said that light is a stream of particles called photons and explains the photoelectric effect and blackbody radiation with this theory - phenomenon which could not be explained by classical physics. This led to the development of quantum mechanics and changed scientific thinking in the 20th century.

he did not actually say that light was an EM wave. maxwell was the one who suggested this and hertz confirmed his theories but planck gave us the properties/nature of light.