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Discussion Starter #1
I have HID and when I switch them to high beam I hear a loud click outside the car. Anyone else have this? You can really hear it when you turn the radio off.
 

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Boltbacker said:
I have HID and when I switch them to high beam I hear a loud click outside the car. Anyone else have this? You can really hear it when you turn the radio off.
Yes. I too have heard it. I believe it only applies to the HID lights. Regular headlights operate on the principal of two different bulbs. One bulb is “regular” intensity; the other is “high” intensity. When you drive without your high-beams the regular intensity bulb is lit and the high intensity is not. When you switch on your high-beams the regular intensity bulb is turned off and the high intensity bulb it turned on.

The HID lights in the Acadia do not work that way. There is only one bulb and one intensity. It does not matter if your high-beams are on or not, the bulb is always on at the same intensity. Instead there is a mechanical device that lowers a shield over the top front of the headlight preventing the light from shinning above ~4 feet. When your high-beams are off, the shield is covering part of the bulb which prevents it from going higher than ~4 feet (this places it just below the rearview mirror of the car in front of you). When you turn your high-beams on, the shield is removed and the light is allowed to scatter much higher, giving you increased visibility.

The best way to imagine it is to turn on a flashlight and shine it at the wall. You will notice a circle of light on the wall. Now cover the top half of the light with your hand. You’ll now see a semi-circle on the wall. Full light is with high-beams on, semi circle is with the high-beams off.

The noise you hear is the mechanical shield shifting back and forth over the path of the light. THE NOISE IS NORMAL.
Park in front of your house at night and turn on the high-beams. You’ll notice the light probably hits the second story windows. Now turn off the high-beams and you’ll clearly see that the top half is covered and light only makes it to the first story windows. But in both situations, the intensity of the light has not changed.
 

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Discussion Starter #4
Ok, sounds good, I wonder why I never heard it on my Cadillac?
 

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Boltbacker said:
Ok, sounds good, I wonder why I never heard it on my Cadillac?
Perhaps your Caddy has a setup like my '98 A8- HIDs are low beam only, with traditional halogen high beams. The system on the Lambdas sounds like a true "bi-xenon" setup (newer Audis have this kind, IIRC). The reason for the "shutter" instead of just turning on a second bulb, is that the HID lights have to warm up when you turn them on. It only takes 1-2 sec, but that's unacceptable when you're cruising down the road.
 
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