Prisoners and the Lightbulb Counter

100 prisoners take turns, one at a time in an arbitrary order chosen by a warden, entering a room with a single lightbulb (initially OFF). Each visiting prisoner may toggle the bulb and observe its state, but cannot otherwise communicate. At any point any prisoner may declare 'every prisoner has now visited at least once'; they win only if the declaration is true. They strategize beforehand. In the standard single-counter strategy, exactly one designated counter increments a tally when he finds the bulb ON (then switches it OFF), and every other prisoner switches the bulb ON the FIRST time they find it OFF (and never again). What total count must the counter reach before he can safely declare everyone has visited?