When purchasing your flashlight, you will most certainly have an idea in your head about how long you plan to use the flashlight at any given time. If you are cave hiking, you can expect to use your flashlight for longer lengths of time (2-3 hours) then if you are using it for a simple family camping trip where you may only use it for a half hour in the evening before you turn on the camping lanterns.
Understanding how long your flashlight will last continuously is different than understanding how long of a lightspan it has. The first correlates to the battery life of the flashlight. The second correlates with how long the bulb and construction will last. Think of the battery life time as how long you expect to have the “on” switch engaged at any given time. Some flashlights can stay on continuously for the equivalent of several days while others may see their light dull after a much shorter duration, like a couple of hours. For your survival, vehicle or earthquake emergency kit, you are going to want to stock a flashlight that can stay “on” for the equivalent of several days (and include additional batteries just in case). For your general household needs you may only need a flashlight that can last for 10-12 hours for your weekend trip. In either case, consider an LED flashlight as this technology offers the longest lasting bulb life of any other flashlights available.
Most any flashlight will offer the battery life data on the packaging or on the web site. Make sure you assess this before making a purchase. It is best to have the right flashlight so always make sure you are getting what you really want.