Assuming this is an incandescent lightbulb with mediocre or poor heat conductivity and that the lapse between "end of the day" and "start of the day" is sufficiently short, extra information can be communicated using the temperature of the bulb (unless it burns out). For example:
The prisoners select a counter, whose count begins at 0 and increases to 1 when he himself enters the room.
When the counter enters the room:
1)If the bulb is off, leave
2)If the bulb is on and relatively cool, turn it off, increment count by 1, and leave
3)If the bulb is on and relatively hot, turn it off, increment count by 2, and leave
When others enter the room:
1)If the bulb is off and the prisoner has yet to signify his presence, turn it on at the end of the day. This counts as signifying one's presence.
2)If the bulb is on and the prisoner has yet to signify his presence, leave it on all day. If the bulb was relatively cool, then this will count as signifying one's presence.
3)If the bulb is on and relatively cool and the prisoner has already signified his presence, turn it off at the start of the day and back on at the end of the day.
4)Else, do not touch the bulb.
When the count reaches 100, he asserts that all have visited.
I suppose yet further information could be attempted to be communicated by toggling the bulb enough to attempt to cause it to burn out and then observing replacements by finding a serial number of some sort, but that's getting outlandish.
The prisoners select a counter, whose count begins at 0 and increases to 1 when he himself enters the room.
When the counter enters the room:
1)If the bulb is off, leave
2)If the bulb is on and relatively cool, turn it off, increment count by 1, and leave
3)If the bulb is on and relatively hot, turn it off, increment count by 2, and leave
When others enter the room:
1)If the bulb is off and the prisoner has yet to signify his presence, turn it on at the end of the day. This counts as signifying one's presence.
2)If the bulb is on and the prisoner has yet to signify his presence, leave it on all day. If the bulb was relatively cool, then this will count as signifying one's presence.
3)If the bulb is on and relatively cool and the prisoner has already signified his presence, turn it off at the start of the day and back on at the end of the day.
4)Else, do not touch the bulb.
When the count reaches 100, he asserts that all have visited.