An entry for ACHOO syndrome in the National Library of Medicine, by a Laura Dean (I think?) from 2012 claims 1 in 4 people will be pushed over the edge to a sneeze when they already have one on the edge, but “pure” photic sneezing is “far less common” although there is no number given, so I have no idea how rare or common it is to just straight up sneeze from light without already having to sneeze
An entry for ACHOO syndrome in the National Library of Medicine, by a Laura Dean (I think?) from 2012 claims 1 in 4 people will be pushed over the edge to a sneeze when they already have one on the edge, but “pure” photic sneezing is “far less common” although there is no number given, so I have no idea how rare or common it is to just straight up sneeze from light without already having to sneeze