You can see the flicker of your light sources for yourself if you have a slow speed camera. iPhone 6s/SE/7 can record at 240FPS. Point that at your LEDs, fluorescents and incandescents. Try your computer screen as well. I did this half a year ago and can confirm. Cheap LEDs are really bad, some more expensive ones don't flicker at all. Cheap computer screens flicker as well. Whenever I find a light source that I don't like somehow but can't quite say why, I record it slowmo and usually it turns out it flickers.