Up to what level of voltage can be used at the switch section of a photorelay?

A voltage to be used should be at a level below the value for OFF-state output terminal voltage V_OFF. Since this is the absolute maximum rating, a state in which it is exceeded even only once must be prevented. For a working voltage, Toshiba recommends up to approx. 80% of the V_OFF value. The specified V_OFF value is written in the technical documents.