Yesterday I had a BBQ with some friends. The sun had already set and the only light source left (besides some ambient light from the world around) was a low energy lightbulb.

After a while I started to see lighting changes in the faces of my friends and the number plates of their cars. It felt like someone toggled the light very fast. When looking at the wall or the light directly I didn't notice any flickering.

In my country the power grid is running at 50hz. Is it possible that I actually saw the flickering caused by the alterations in the power grid or am I just going insane?

Ps: sorry if this is the wrong site. Didn't know where else the question would suit.