LEDs, or light emitting diodes, have become more and more popular lately as awareness grows of their many benefits and advantages over traditional incandescent lighting. LEDs typically use about one tenth of the energy used by traditional light bulbs. Since they're solid state, they are also far more durable, and will outlast any traditional light bulb currently available.
Light emitting diodes have many uses, and one of the most common is in flashlights and headlamps. LED flashlights come in all shapes and sizes, from tiny models that fit on a key chain, up to 12v rechargeable spotlights. Small LED flashlights can last thousands of hours, and are powered far longer on a set of batteries than a traditional flashlight.
Small headlamps are also very common, particularly among campers and backpackers, as they're very small and light weight, and quite convenient for hands-free use. These headlamps can cost anywhere from $15 to $300 dollars. They're quite handy to keep in your car or toolbox in case of emergencies.
LEDs are also used more and more in automobiles, both as tail lights and for more decorative lighting. Obviously, since LEDs are so efficient and durable, they're nearly perfect for use as tail lights. One set of LEDs can easily last the life of the car and avoid replacement entirely. It's more difficult to use LEDs for headlights because they only produce light in one direction, as opposed to lighting in all directions where it can be focussed by a reflector. They are gaining traction for this application, however.
Decorative lighting for cars and motorcycles is also a very popular application of LEDs. They're easy to install, particularly in tight spaces since they're so small. They also come in a wide variety of colors, and are commonly used for under car lighting, dashboard lights, and even door handles.