Thread: HID conversion

Originally Posted by BMKal

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And to dispel an old wives tale - provided that the actual light source is in the same position relevant to the reflector - it is physically impossible for the light "pattern" spread by the reflector to be any different. ALL light travels in a straight line, and when it strikes a reflective surface - the angle of reflection is equal to the angle of incidence - simple basic law of physics. The ONLY way that a reflector can give off different light patterns is when the light source is in different positions relative to the reflector.
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Tungsten filaments are straight and horizontal so that it is impossible for a HID to occupy the same position, since an HID arc will always be bowed into a curve due to the effects of convection. How big this effect is will depend on the geometry of the reflector and lens.

John

Yes - agree with you there John that the two light sources may be a different shape. But when you look at it, each actual light source is not much more than a quarter of an inch long.

I disagree with you though that it is impossible for a HID to occupy the same position. I have closely compared the position of the HID light source in mine with that of the halogen globes previously fitted, and as near as I can measure it, the light sources occupy the same position.

While the shape of the source may be slightly different, I hardly think that this difference over such a short length would have any noticeable difference on the reflective pattern, given the ratio between the size of the light source and the diameter of the reflector. In fact, on mine the light pattern in front of the vehicle appears to be pretty much the same with either light source. The noticeable differences are in the colour / clarity of the light, and the HID tends to have a much more distinct low beam "cut-off" than the halogen did, though it may be just the that you can see it more clearly.

I did note that I had to adjust my headlights down quite a bit more than they were previously set at when I installed the HID to avoid "glare" to oncoming drivers - but once this was done, I have not had a single oncoming vehicle "flash" me, and I still have much better vision on low beam than I ever did with a range of halogen globes that I tried. I'm a fussy bugger when it comes to keeping my headlights (and windows) clean as well. While I have never noticed excessive glare from HID with dirty headlight lenses myself, I have read on here and elsewhere that this is a possibility - hence the legal requirement for headlight washer / wipers.

Believe me - if I thought for a minute that my headlights were dangerous or causing a nuisance to other road users, I would change them back in an instant. I carry a set of halogen globes in a packet in the glovebox, and it is a 5 minute job to change them over the way that they are set up in mine (the original wiring and plugs are all still in place). But so far, I've never had any cause at all to believe that there is any problem with them - including swapping cars with the Mrs (Camry) and driving towards each other at night so that I could see for myself what they look like to oncoming traffic. They're very white, yes - but not annoying, even in wet weather conditions.