Similar to fluorescent lights, HID lamps need a ballast (a device used to start gas discharge in a lamp and limit the flow of electrical current) to even start producing heat. If they don't have the ballast, the reaction won't begin, and there won't be any light.

In a Simpler wordings, HID is the upgraded lighting kits from the original halogen bulbs, it's getting more popular this few years, as most of the new car models are all equipped with the HID Light Kits.
Advantages for HID Lights :
- Greater output of light , can up to 3 times brighter than a halogen bulbs
- Cover almost 70% of the road , have a better vision when driving.
- Greater Durability, withstands a greater amount of vibrations and shocks.
- Greater bulb lift, can last up to 4-10 years or 3 times longer than a original halogen
bulbs.
- Lesser power consumption, save up to 25%.

Color Temperature:
HID Color temperature refers to the degrees (K) , which simply the measures of the color for the lighting output, like golden yellow, white, crystal white, blue ?
Degree (k) refers only to the color, while lumen refers to the lighting intensity. So the higher the color temperature (degrees K) doesn't mean a higher light intensity (lumen). Here is the summary for the common color temperature on the market --
3000K (Golden Yellow) , 4300K (Bright White), 5000K (white), 6000K (Crystal White),8000K (Crystal Blue), 10000K (Aqua Blue), 12000K (Purple-Blue).