tommudd wrote:
Coming from someone who has driven almost a million miles in a Peterbilt , yes those DA** lights will blind a truck driver
Thats one of the reasons I had a spot light trained to the left side of the lane beside me, worked great when someone came up along side with HIDs
by the way
Halogen headlamps and HID headlamps require very different optics to produce a safe and effective—not to mention legal—beam pattern. How come? Because of the very different characteristics of the two kinds of light source.
A halogen bulb has a cylindrical light source: the glowing filament. The space immediately surrounding the cylinder of light is completely dark, and so the sharpest contrast between bright and dark is along the edges of the cylinder of light. The ends of the filament cylinder fade from bright to dark. An HID bulb, on the other hand, has a crescent-shaped light source -- the arc. It's crescent-shaped because as it passes through the space between the two electrodes, its heat causes it to try to rise. The space immediately surrounding the crescent of light glows in layers...the closer to the crescent of light, the brighter the glow. The ends of the arc crescent are the brightest points, and immediately beyond these points is completely dark, so the sharpest contrast between bright and dark is at the ends of the crescent of light.
When designing the optics (lens and/or reflector) for a lamp, the characteristics of the light source are the driving factor around which everything else must be engineered. If you go and change the light source, you've done the equivalent of putting on somebody else's eyeglasses: You can probably make them fit on your face OK, but you won't see properly.
Why H.I.D. light bulbs don't work as good in a headlamp designed for a Halogen bulb.
It actually has to do with where the light source reflects it's light onto the lamps reflector.
If the light bulbs light doesn't hit the correct focal point of the lamps reflector then the light gets scattered causing an
unfocused beam pattern*.
This is what happens when you install a H.I.D. bulb into a Halogen headlamp housing, the arc of the illuminated H.I.D. bulb is just outside of the headlamps reflectors optimal focal point*.
Automotive headlamps which use a standard Halogen light bulb such as a 9000 series or an H 4 variety are designed
around the bulb.
The same for a high intensity discharge bulb. The headlamps reflector/projector lens is designed around the bulb.
The light that gets reflected onto the road is better than that of a standard Halogen bulb but the stray light that is cast everywhere else is a nuisance to oncoming drivers