Very interesting question, it is true that light is pure energy. But why?
Energy of any source stored in waves and if the wavelength of a source wave remains almost same during propagation then it is called pure energy it is possible only if source has no mass.
It is true that light is the simplest electromagnetic wave. It Can be seen from EM spectrum that Light spectrum is the many different wavelengths of energy produced by a light source. Some are visible and some are invisible etc. This classification of spectrum is based upon wavelength. The purest form of light energy is Laser light because it remains steadily at almost the same wavelength.
Ref. Definition:
"Pure energy is any field energy, like potential energy, any kinetic energy, like a fast moving particle, but no mass energy of stable or nearly stable massive particles which would require a process to turn into work. Light is a form of energy but has no mass". Thanks
Light is not the simplest electromagnetic wave. All electromagnetic waves are just as simple and just as complicated. Light and all electromagnetic waves have linear and angular momentum, as well as energy. The only significant difference between visible light and other electromagnetic waves is that humans have detectors in their eyes that can detect visible light and distinguish 3 different frequency bands. This is possible because photons of visible light generally have enough energy to move electrons about in organic chemicals, which means the sensors in our eyes can work. They don't generally have enough energy to break chemical bonds in organic chemicals, which causes damage and cancer.