It is a visible form of energy to the human eye. Plants need light to grow. They use a process called photosynthesis . Light can behave like a wave sometimes and then like a particle at a different time.
Photons are particle-like features of light.
Photons always move at 186,000 miles per second and have no mass. The time that light shows a wave-like behavior is when it defracts. The building blocks of matter are atoms. We can hear sound when it has frequencies between 15 and 20 thousand hertz . Ultrasonic sounds are higher than 20,000 herts.