It's actually a well known effect. Astronauts have reported seeing flashes of light when they close their eyes in space. It's believed to be caused by Cherenko

It's actually a well known effect. Astronauts have reported seeing flashes of light when they close their eyes in space. It's believed to be caused by Cherenkov radiation from cosmic rays traveling through the vitreous humour of their eyes. Source: https://www.nature.com/nature/journal/v228/n5268/abs/228260a0.html https://www.nature.com/nature/journal/v228/n5268/abs/228260a... https://www.ncbi.nlm.nih.gov/pubmed/12678106 https://www.ncbi.nlm.nih.gov/pubmed/12678106