flicker of lights

Flickering lights can also cause some people to have epileptic fits or bring on migraines.

We had one odd incident here in Montréal when a our tunnel crossing to South Shore was renovated. The tunnel is quite long and was always kinda dark. So, the city decided to put in much more lights. Unfortunately, the lights were placed in such a way that going through the tunnel at the speed limit created the same speed of flikering required to trigger epileptic seizures and migraines.

I didn't know that was what was happening but had taken to avoiding the tunnel since I'd always come out with a migraine on the other side.

It was only when they finally fixed it and the explanation appeared in the papers that I understood why it was happening.