What are the differences between Fenix flashlight designations such as E, PD, LD, etc.?
Those letters used to represent more precise categories but as more lights have been released, they haven't been quite so clear. We generally define them as you can see below. Remember that these rules may not apply to all lights in a series.
E Series: These are normally more of the entry-level lights. Most of them have a simple interface, without a lot of output modes. Many are key chain lights.
FD Series: These have focusable lenses. They will go from a spotlight beam to a flood beam.
LD Series: These started being the lights that ran on alkaline batteries. Over the years, they have started to include Ni-MH batteries and other types.
PD Series: These are overall our everyday carry lights. Small and very powerful.
RC Series: Rechargeable
SD Series: Dive lights.
TK Series: Tactical flashlights
MC Series: Adjustable multi-angle
UC Series: Rechargeable, most using a micro USB cable.