Can seizures be triggered by flashing lights?

Yes. The routein EEG usually includes a flashing light segment to see if this brings out abnormal brain wave activity that could be related to seizures. Eeg studies without this segment are considered incomplete.
Classic but rare. Photosensitive epilepsy has been known for decades. Good quality eeg includes flashing lights to see if seizures can be induced. It has been the subject of extensive studies of how the brain responds to certain stimuli. Old tvs and old video booths were often at fault. Newer equipment has significantly reduced the occurrence.