Not by the lights themselves but looking through the eyepiece at the image reflected from the rotating mirror on the camera. Generally a 180deg. 24 FPS flicker that would give me a headache after a few hours.

Our eyes and brain are amazing. I was shooting a whichcraft film in Salem Mass.. We had a 12 foot pentagram on the floor that was lit from below by lights and had a primary green gel on it. All the light was primary green. After a while the green went away replaced by a kind of grey. We had a class of school kids around the green circle and I asked the electrical crew to backlight some of them to separate them from the background. They put a light on and it was primary red. I told the to take the gel off and was told that there wasn't any gel on it. My brain had corrected out the green shifting everything making a white light red. Really weird. I realized that the only way to tell what I was doing was using the readings on my color temperature meter.

There was a UCLA study back in the 80's where a student put on glasses to inverted the image. On the 3th day he woke up and everything had corrected it's self. When he took the glasses off everything was upside down.

Those are gross examples and I could be full of s--t but believe that our brains are registering a lot that we're not aware of. Whether or not it makes an impact on us is an individual thing. I'm a bit like GeneC. I see flicker when others can't. The best way is to not look directly at it but through your peripheral vision.

I'm also somewhat color blind. (imagine that, a DP that's color blind.) I took an 'Ishihara Test' and found that out. The image below has a large number on it. If you can't see the number you're red/green color blind. I can see it although not easily. If I didn't know it was a 6 I couldn't do it. Therefore, I couldn't get a captains license. Hell, that may be from all those bright lights and flickering shutters.

http://www.toledo-bend.com/colorblind/Ishihara.asp