You can test it by yourself here
The effect is remarkable for often lasting an hour or more, and in some cases after prolonged exposure to the grids, the effect can last up to three and a half months.
Woah, what a migraine inducing effect. I'm not even joking -- my head hurts after watching these images for 30 seconds. This is pretty interesting, nevertheless.
If you're into headaches I recommend checking this post as well.