Battery powered flashlights are not a recent invention, and have been around since about the last years of the nineteenth century. Over time flashlights have gotten increasingly sophisticated and have branched out into being used for various activities. Their designs, complexities and intensities are all different depending on the work.
Earlier flashlights used to have incandescent bulbs in them consisting of a glass bulb with a tungsten filament in a vacuum, which are increasingly being replaced by the new LED technology. While LEDs have been around for many decades (mainly as light indicators), they ve now been incorporated into mainstream lighting. These are an order of magnitude more energy efficient than the earlier ones.
Specialised designs of flashlights are used depending on the need. A medical halogen penlight is used to observe the pupillary reflex, the headlamp is used by trekkers, miners, and people working in construction sites, a diver s lamp is completely waterproof which generally can be attached to the diver s suit to see underwater while non incendive flashlights are used in inspection of areas full of flammable gas.
For each industrial use, there are worldwide and national standards that flashlights have to adhere to after which they can be incorporated.