Filaments: Standard VS HIR (Halogen Infrared Reflective)
Halogen Infrared Reflective (HIR) technology came along before xenon and after the first halogen based bulbs came out. All headlight bulbs were still filament based bulbs at the time and the arc tube hadn’t yet been invented. The improvement did some great things to improve the brightness in the bulb.
Filament based bulbs undergo what’s known as the Halogen Cycle or Tungsten Cycle, where the residue on the inner wall of the bulb is redistributed back on to the filament, keeping the bulb clear. Without this cycle the bulb would cloud up like a normal bulb and the brightness of the bulb would drop significantly. While this isn’t that big of a deal for a normal light bulb in your house where you can just replace it easily, a headlight for an automobile needs a much longer bulb life.
With the Halogen Cycle the brightness of the bulb does not drop, but it doesn’t get any brighter either, which is what developers were trying to accomplish with HIR technology. HIR uses a round bulb instead of a conical one. Most Halogen bulbs up until this time were shaped in a way to project the light outwardly and thus the bulb was not round. And it might seem intuitive to want a projector like bulb, but not with HIR.
Halogen Infrared Reflective technology is these three words. (1) Halogen: the bulb uses a halogen mixed in an inert gas to help the filament burn brighter and help redeposit the tungsten from the bulb wall back onto the filament. (2) Infrared: the inner wall of the bulb is lined with a special material that allows visible light to pass through and infrared light to be trapped inside. (3) Reflective: the visible light that escapes the bulb is reflected in the direction (forward) that the headlight is designed for.
So what’s going on here is the round bulb with the special coating on the inside keeps the infrared light in and let’s the visible light escape. The infrared light bounces back and hits the filament again and again and causes it to get even hotter and burn even brighter without needing to use more energy, less in fact for the same amount of brightness. Then the light is reflected to where it needs to be aimed.