It might be worth mentioning that their older lights used a slightly different layout - the current LD10 is the replacement for the L1D for example.
There also used to be the LT series (L1T and L2T) which I believe were named L (standard batteries) - amount of cells used - T (Tactical? Both were simplified lights without all the fiddly modes of the L1D).
You will also see quite a few lights with the emitter tacked on to the end of the name to denote revisions of the same light where they have updated the emitter but kept everything the same.
I was looking at them the other day and was wishing they had kept the 'L for standard, P for lithium' naming with the TK series - at a glance it is impossible to tell which use AA and which use CR123 batteries.