Shut it down or let it run?

I just recieved an Hitachi CP-s230 LCD projector to use in my classroom.

I use it all day but there are periods during the day when it is idle.

My question is: Does restarting the lamp put wear on the over all life of the lamp. Someone told me "striking" or firing up the lamp was the equivilant of X hours of projection.

Is that true? Would it be better for me to leave the projector projecting through my lunch break for example?

Thanks.