High-intensity discharge (HID) and light-emitting diode (LED) are two different light sources. Which one is better depends on what the light is being used for.
HID: How It Works
HIDs produce light with a current passing through a metal vapor, which eventually produces radiation. These lights require a ballast to stabilize the flow of this current.
LED: How It Works
LEDs use semiconductor diodes that emit light when connected in a circuit. These lights are stored in a plastic bulb for concentration of the light source.
Advantages of HID over LED
HID lights are much brighter than LED ones. This is because their side-emitting light is easier to focus than the LED's is.
Advantages of LED over HID
Unlike HIDs, which need about 15 to 25 seconds to warm up during ignition, LEDs go on instantly. They are more durable than HIDs and can last thousands of hours longer.
If you need lighting of great intensity and tight focus (especially for diving purposes), HID is the way to go. LED, however, is the more common light source, ubiquitous in its application in modern society, from traffic lights to DVD player lights.