Stroboscopic 40 Hz flashing light devices can cause side effects including nausea and headaches.
"Most use what's called stroboscopic light, and that's the type of light that flashes then you can see the flashing and that can cause nausea, it can cause headaches" (said at 0:28:13)
No published records detailing the specific adverse event rates (such as nausea and headache) associated with visible stroboscopic 40 Hz light stimulation devices were successfully fetched within the search limit. Consequently, the claim cannot be independently verified from the retrieved records.