It's a single physical thing. Light is only singular as a concept. When you observe light it's always different. The sunlight you see today isn't what you saw yesterday. We also see different kinds of lights like the computer/mobile screen, sun, torch, fire etc. I'm asking for "just 1 thing".

English isn't my native tongue either. It's the age of internet. If there is anything you don't know, just type it on a search engine and press enter :-)