The 2006 Sierra left the factory with halogen bulb reflector housings. This design uses a mirrored bowl to focus light from a single-point filament. The key to any successful upgrade is respecting this optical design. Simply plugging in a random aftermarket bulb can be disastrous. The most common misstep is installing HID (Xenon) bulbs into these stock housings. The arc of an HID bulb is in a different location and emits light in a 360-degree pattern, which the reflector scatters uncontrollably. The result is a blinding, illegal glare for oncoming traffic, while often creating dark spots in your own field of view. For a truly high-performance, road-legal result, you must address the entire optical system, not just the light source.



