Many books including the book (Hamamatsu, "Photomultiplier Tubes", http://astroa.physics.metu.edu.tr/~umk/astr517/Hamamatsu_PMT.pdflink to PDF) says that a photocathode of a photomultiplier tube is damaged by intense light.
Do not expose to strong light. The photocathode of photomultiplier tubes may be damaged if exposed to direct sunlight or intense illumination. Never allow strong light to strike the photocathode.
Buy why is it damaged by intense light? Surely, intense light causes excessive photocurrent and many electrons will be emitted from the photocathode of photomultiplier. Why does a large current damage the photocathode?
