Full Idea
Planck had assumed that light is emitted in quanta called photons. Einstein went further - light is photons.
Gist of Idea
Light isn't just emitted in quanta called photons - light is photons
Source
Frank Close (Theories of Everything [2017], 3 'Light!')
Book Reference
Close,Frank: 'Theories of Everything' [Profile Books 2017], p.48
A Reaction
The point is that light travels as entities which are photons, rather than the emissions being quantized packets of some other stuff.