Incandescent bulbs are the most common type of flashlight bulbs because these are the bulbs that usually come with a flashlight when you purchase it from the store. The bulb is made of glass and has a small metal base attached to the bottom. You can also find replacement bulbs without any base, or with a base that is made of glass. These are available in different types including Krypton, which burns brighter but doesn't last very long, and Halogen bulbs, which are more expensive but last longer.
LED bulbs are gaining in popularity because the bulbs are more energy efficient than other types. The bulbs can last up to 10 times as long as an incandescent bulb, though you'll also have to pay more money for this type. Another advantage to using LED bulbs is that they come in a wide variety of colors such as red, green, blue and amber. The red bulbs work in emergency lights as well as flashlights, and also work in regular flashlights to provide better clarity at night.
Fluorescent bulbs are much more expensive because this type wasn't designed for traditional flashlights. Yet there are some flashlights and outdoor lights that now use this bulb. They are harder to find, though most electronics stores now sell them. The bulbs are longer and usually curved to fit the inside of the light. You can only use these bulbs in lights that use fluorescent bulbs originally and not as a replacement bulb in a traditional flashlight.