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In Reply to: Question posted by on xenons (m) on August 13, 2000 at 18:08:59:
Comparing the bare lamp , the lumen output for halogen filament lamp is about 1200 lumens operating at 55 watts. Lumen output for HID is about 3200 lumens operating at 35 watts. THat's a 3x increase.
However, a bare lamp's light output is rather useless in the real world. How much light is controlled, redirected, and shaped by the headlight fixture is more useful and is measured in terms of efficiency.
Efficiency of a headlight using halogen lamp is about 25% efficient whereas efficiency for HID is about 60%. Thus, 1200 lumens x .25=300 lumens outputted for halogen, whereas 3200x.6=1920 lumens output for HID. The increase in lighting from Halogen to HID is on a factor of 6x when the entire lighting system is calculated.
These are ballpark numbers...other factors such as dirt accumulation, lamp efficacy, and lumen maintenance is left off for simplistic comparison.
The other intrinsic component of valuation is that of visual comfort. Visual comfort measures the existence of glare control. The higher the visual comfort probability, the less fatigued the eyes become. The HID excels in this area due to a smaller and more compact light source discharged from the arc gap. Compared to the halogen's filament winding, HID lamp imaging is 10 times smaller in displacement. Lighting designers have more room inside of a headlight to control a smaller lamp image than than they do with a larger lamp image. And in a roundabout way, when more lamp images escape the light housing for the HID over the halogen's imaging, efficiency for HID is invariably higher.
Thus, the way I see it, light output increases 6x, with 20 less watts consumed per lamp, and increased visual comfort due to reduction of glare and precise ray aiming and lamp life for halogen is somewhere around 100 hours whereas HID is presumably for the life of the vehicle.
I recognize they may improve night vision somewhat - perhaps even substantially. Do you think that the improvement is significant in terms of safety, or that it doesn't matter that much - i.e., that the standard headlights provide enough illumination and the benefits of xenons, even if substantial in absolute terms, don't make the car that much safer?
2. Does anyone have any information on whether xenons are apt to blind on-coming traffic? I know the BMW xenons are supposed to remain pointed more or less at the road; I wonder if they really do this or if they pose essentially the same hazards to on-coming traffic as other manufacturers' xenons.
Thank you in advance for your observations.
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