Each lamp is designed to use one kind of bulb. That decision is made when the lamp is being engineered. There are certain kinds of bulbs that can be replaced with certain other kinds in certain lamps without causing problems, but for the most part yes, you do have to replace it with the same kind. The number (H1, H2, H3, H4, etc) does not indicate better/worse or anything else about the characteristics of the bulb; these numbers are issued sequentially. H1 came in 1963, then H2 in 1964, then H3 in 1966, H4 in 1968-69, H5 and H6 exist in theory but were never adopted, H7 in 1992, etc. Meanwhile the US devised its own numbering system in 1983 with HB1 ("Trade number" 9004), HB2 ("Trade number" 9003) in 1992, HB3 (9005) and HB4 (9006) in 1985, and HB5 (9007) in 1991. Then the US authorities stopped trying to buck the system and the industry moved toward worldwide light sources so H13 is H13 all over the world, only someone (at Ford, I think) arbitrarily decided to call it "9008" even though there's no such trade number, so now there's a trade number 9008...confused yet? Replace the bulb in your headlamp with the same kind of bulb.