Light is not considered as matter, but rather as electromagnetic radiation. It exhibits properties of both particles and waves, which can sometimes lead to confusion. The concept that light can behave as both a particle and a wave is known as wave-particle duality.
In certain experiments and observations, light behaves like a particle called a photon. Photons are discrete packets of energy and can exhibit particle-like properties such as being absorbed or emitted in discrete amounts. For example, when light interacts with matter, it can transfer energy to electrons in a process called the photoelectric effect.
On the other hand, light can also exhibit wave-like behavior. It can undergo interference, diffraction, and polarization, similar to other types of waves. For instance, when light passes through a narrow slit or around an obstacle, it can exhibit wave interference patterns.
The wave-particle duality of light is a fundamental aspect of quantum mechanics, which is the branch of physics that describes the behavior of particles at the microscopic level. This duality is not exclusive to light; other particles, such as electrons and protons, also exhibit similar dual nature.
It's important to note that when people refer to "matter," they are usually referring to particles that have mass, such as atoms and subatomic particles like electrons and protons. Light, being massless, does not fall under the category of matter in the traditional sense.