Apollo 17 crew reports cosmic-ray light flashes in cabin — translunar and transearth coast

All three Apollo 17 crew members (Cernan, Evans, Schmitt) reported seeing light flashes inside the darkened cabin throughout the mission. CDR Cernan described streaks, spots, and a very bright headlight-like flash. These phenomena are consistent with cosmic ray or high-energy particle interactions with the retina (Cerenkov radiation or direct retinal stimulation), a well-documented phenomenon in spaceflight. The ALFMED experiment was designed to study exactly this phenomenon.

“CDR Cernan: "the one most imposing thing I remember... was the fact that there was a very bright spot that flashed right between my eyes like a very bright headlight - like a train coming at you, only with a flash." / SCHMITT: "We had light flashes just about continuously during the whole flight when we were dark adapted."”

OCR quality is good. These light flashes are a well-understood phenomenon in spaceflight (cosmic ray/high-energy particle interaction with the eye), corroborated by the ALFMED experiment referenced in the transcript. Included here because they are logged as anomalous visual phenomena by the crew. Mission elapsed time spans the full flight.