Have you ever seen something like a flash light?

Ok, it’s kinda weird but I’ve experienced this three times already.
The first time I was in my bedroom, at night, I have blackout curtains so, my room is completly dark at night, no lights can be seen from the outside, so once, suddenly I saw this light, like the flash of a camera, it lasted just a second but it was a very bright light, it illuminated the whole room for that tiny moment.
The second and the third time also, I was in my office, at noon, with my co worker, and again, that flash light out of nowhere, and me and my friend saw the very bright light.
Maybe, it’s nothing, maybe not, but im just curious, since a googled it and many people have seen it too.

Have you? or what could it be?