Which theory was contradicted by experiments with the photoelectric effect?

Wave theory of light that states that visible light irrespective of its color, can cause the ejection of electrons when it strikes a metal.

Explanation:

Wave theory of light:

If we go through wave theory of light, it clearly focuses that light is of actually wave nature not particle nature. The wave theory was based on the ideas of Hertz who discovered in 1887 that metallic surface can emit heat energy (electrons) when light hits the metal.  If we increase the intensity of light, it will also increase the incident energy and ultimately increase the kinetic energy of electrons.  Moreover, the frequency of light do not matters much, just a beam of light can eject the electrons from the metal.

Photoelectric effect:

On the other hand, Photoelectric effect can be considered only if we assume that light has particle like nature and not wave like nature.  

It also says that frequency of light matters alot in ejecting the electrons from the metals. If the frequency of light is less, it will not eject electrons from the metal surface even if it falls on metal for a very long time.It also says that  maximum kinetic energy of the electrons (that are emitted) corresponds with the light frequency that caused the emission of electrons.The current of emitted electrons is directly proportional to the intensity of light that caused the electron emission.

We can see that the postulates of wave theory (like no.3) are just opposite to the postulates of photoelectric effect. The photoelectric effect also explained the relationship between emitted electrons and light in a better way that was not described by wave theory. We can say that it is as advanced explanation of facts based on the classical theory of wave like nature of visible light.