Intensity Discharge light ( HID Lights ) globes are super bright compared to
the regular halogen light globes.
This type of light is widely used in Europe and is starting to be an option and standard on newer vehicles in Australia; spots are available in the HID version, and conversion kits are available for most makes and models.
A HID-light require fewer watts and produce more lumens than a conventional halogen light.
In comparison a set of HID-lights can produce over 3000 Lumens from under 40 watts as a posed to Halogen using 70+ watts to produce 2000 Lumens. These figures are approximate and just to state the overwhelming lumens to watts difference between HID and Halogen lights.
The average life of a HID lamp is about twice as long as Halogen, HID's can keep going for around 2000 hours.
The light temperature on a HID-light is between 4000K - 5000K which produce a white to blue colour light.
The light temperature of Halogen lights is between 3000K - 3500K
HID-lights draw less power from the alternator and battery which will save power, but the cost of HID when compared to Halogen will more than likely out weight the cost savings in extra fuel (petrol/Diesel) burnt for running the alternator longer/harder.
HID-lights are more expensive than the Halogen and LED lights, for the extra money spent the difference in lighting is just as noticeable.
HID-light beams travel much further than Halogen and LED lights.
If driving the country roads often after dark then a good set of HID spot lights is money worth spent.
When a halogen headlight is retrofitted with a HID-lights conversion kit, the light spread and output will be altered. This could blind oncoming traffic potentially causing an accident.
In Australia a HID-light conversion kit will make the vehicle un-roadworthy/not street legal.
Unless the manufacturer of your vehicle has made this an optional extra or release HID-Lights for your make and model it won't be street legal.
HID spot lights are however legal if electrical switched and mounted correctly.