Albert Einstein about light

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1. Light was historically regarded as waves, because it undergoes wave properties such as interference, diffraction and refraction.

2. Einstein postulated that light was emitted in the form of quanta, which are discrete packages of energy. In other words, light is in the form of particles, which is now called "photons".

The energy carried by each photon is proportional to its frequency. Hence, photons of violet light is more energetic than those of red light.

3. Using the concept of photon, Einstein sucessfully explained the "photoelectric effect" and dicovered the law governing it. This achievement brought him to the award of Nobel Prize in Physics in 1921. His quantum postulation of light also threw insight into the field of quantum physics that was developing at that time.
4. see answer to (3) above.
5. Solar cells, or photoelectric cells, utilize the principle of photoelectric effect in their operation. These devices have been used widely in many areas, including in space exploration. Since solar, or light, energy is a renewable energy that would not cause any pollution in its production, it is believed that the uses of solar, or photoelectric, cells would become more versatile in future.

6. Einstein's idea gives the "dual nature of light" concept, i.e. light behaves as waves and particles. This concept has been widely used in the development of many branches of modern physics.

I want to ask about Albert Einstein's contribution.
In fact, Einstein's famous contribution in physics is on the Special Theory of Relativity (特殊相對論) and General Theory of Relativity (廣義相對論), in which he revolutionized the concept of space and time, and gave a new insight in gravity.