According to the electron-cloud-conductor model, there should exist interaction of electromagnetic induction between light and electron when they meet, and this interaction may result in the energy exchange between them. Energy exchange between light and free electron in vacuum is analyzed with the model, and the result consists with that of the existing theory. The model can also be used to explain the experimental result of ionization rate of N2 molecules by short laser pulses and the behavior of ionization of molecules by X-ray. It is concluded that one of the root causes for energy exchange between light and an electron is electromagnetic induction between them.