Every Day Carry (EDC) pocket lights-
This class of flashlight increases it's utility by being carried in such a way as to be most often available in times of emergency. In order to fit in this class, the flashlight must be easy to carry. This requires a certain size limit and ergonomic design features.
This class can be attached to a key chain or placed loose in the pocket (although is must be comfortable in the pocket). Models in this class are no bigger than 3" long and 1" in diameter (weight is 2 oz inc battery). It must be easy to carry, access and operate. A flashlight that requires too much thought or effort to bring along with you does not fit in this class. Most of the best lights in this class use LEDs which last almost indefinitely.
This class is most likely to save your life and count in an emergency because it is with you most of the time. However, this class is typically not bright enough nor flexible enough for more intensive missions, which brings us to the next class.
Mission lights (larger units)-
This class of flashlight is not as easy to carry in the pocket as the EDC class. We make the decision to take it along because it is usually brighter and/or provides more features. The extra effort required to take it along usually means its inclusion is part of a plan or mission. There are different sizes of light in this class such as a duty light, head light, lantern, work light, glove box light, etc, and all are commonly pre-staged in a backpack, vehicle, tool box, boat or mounted on the wall next to the back door.
Not all lights in this class are brighter than the EDC but they are all larger. Much longer runs times are possible by incorporating multiple batteries, often running many hours or even days.
One type of light in this class would be a combo light with multiple LEDs and filament bulb in one unit. This type of flashlight allows for long run times when running on the flood-type LEDs, or when needed, a bright Xenon beam can be accessed by simply pressing a button.
Tactical lights (very bright units)-
Models in this group are surprisingly bright. They are referred to as "tactical" because they are used by law enforcement/military to temporarily blind a subject. They provide a debilitating beam that stuns and has lots of reach.
While some of these units are quite small, some people find them uncomfortable to carry in their pants pocket on a daily basis and therefore are not small enough to be included in the EDC class. These very bright (minimum 65 lumens) mini-models are excellent second lights to have readily available. Most tactical lights still use filament bulbs.
Much bigger in size and power are the models usually sold to law enforcement and the military for perimeter security around installations such as nuclear power plants. These expensive lights have extremely powerful beams (250 lumens or more) and are much too bright for use inside a home. Due to their huge energy draw they have fairly short run times.
Also included in this class are the specifically designed weapon-mounted flashlights. These units can be left attached to the weapon or can be removed for carry in a belt holster.
Speciality flashlights-
These are lights that do not fit in the previous classes but are still man portable. In this group you might find infrared units, UV models, blue lights for tracking blood, red for retaining night vision, strobe/signal models, etc.
For most folks, the idea of spending a hundred bucks on a flashlight is beyond consideration. But once they see a high-end LED in action they're often more willing to meet the idea halfway. It's then easy to see that tiny LED 'lights can be very useful every day tools.