Halogen bulbs are similar to incandescent bulbs, except they have an inert or halogen gas added. They burn brighter; use bulbs of the same intensity on both sides of the vehicle. Because these bulbs contain halogen, it's important not to touch the glass portion of the bulb with your fingertips. The tip may be coated with a dark material, but it's a good idea to handle these bulbs by the base. Older headlight system's used sealed headlamps that had the bulb contained inside the headlight. They were usually much more difficult to replace. Still some of these (HID) high intensity discharge bulbs can be difficult, and if it's necessary to touch the glass (it shouldn't be) always use gloves or a piece of paper to handle the glass portion of these bulbs.