How often (with normal use) do you have to change the bulb in a projection LCD tv?

I was told about every 3-4 years, and I think the guy at the store was trying to sell me a service plan using this bulb thing. My father has had an LCD projection tv for about 4 years now and he has never had a bulb problem. Any help would be appreciated.How often (with normal use) do you have to change the bulb in a projection LCD tv?I think the seller was right. The bulb in the projection tv's loses its freshness two years later. It depends on your usage style, of course. but in general, the projections have less lifespans than plasmas, lcd's and other type of image sources.