Light is electromagnetic energy. When charged particles vibrate, they create electric and magnetic fields that vibrate. Electric and magnetic fields are spaces in which the force (push or pull) of charged particles and magnets have influence without contact (i.e. objects in the field can be pushed or pulled without being touched). Waves are simply motions caused by vibrations. The waves resulting from the vibrations of electric and magnetic fields are called electromagnetic waves and the energy these waves carry is called electromagnetic energy. Electromagnetic waves can travel in a vacuum (i.e. their motion is independent of a medium) and they all travel at the same speed (the speed of light, 300 x 106 meters/sec in a vacuum). The following electromagnetic waves arranged in order of increasing wavelengths constitute the Electromagnetic Spectrum: radio waves, infrared, visible light, Ultraviolet, X-rays and gamma rays.
In order to explain the photoelectric effect of light, scientists have characterized light as being particle-like in addition to being wave-like. They call the particles of light, photons.
The charged particles, the vibrations, the electric and magnetic fields, the waves, the photons and the energy, are all expressions of Pj problems. Consequently, light is an expression of Pj Problems.