There are a lot of bulbs being sold on eBay - and in local stores - that are advertised as "Xenon", "HID simulation", "Plasma", whatever they are called, that promise "Brighter light!", "55w -> 90w", "Improved visibility", "more efficient", etc.
Are any of these claims true?
After both reading about the bulbs (www.danielsternlighting.com , a very informative site, among others) and trying them out in my own vehicle, I have a pretty good idea what these bulbs really do. First off, they do not use "Plasma" as they are sometimes called.
Here's a quick lesson: True HID (high-intensity discharge) systems use an arc of plasma to create the white, bright light they are famous for, producing light above 4000 Kelvin in temperature usually up to about 6000K, although there are some systems that produce light upwards of 10,000K (although this produces a violet-colored light which is very dangerous). HID systems put out MUCH more light than a halogen system and because of it, they have more focused optics to avoid throwing light all over the road and blinding drivers. While improving illumination in the immediate foreground, the sharp cutoff makes it more difficult to see objects farther down the road, out of the light's projection.
Halogen systems have a bulb that produces light around 3200K, which is the familiar yellowish-white we are accustomed to seeing. Halogens are not as efficient as HID systems, with a typical 55 watt halogen bulb producing around 1000 lumens. In contrast, the HID bulb puts out around 3000 lumens and only consumes about 35 watts, making them tremendously more efficient.
So here's where the "Xenon" or "Plasma" bulbs come in. They promise a higher color temperature and the increased visibility of HID, at the price of a regular halogen bulb. Look, there is no free lunch, and if it sounds too good to be true, it probably is. These "Xenon" bulbs just have a bluish layer added to a regular halogen bulb's glass, filtering out the yellowish rays and making the light whiter. The problem here is, because its filtering out some of the light, the amount of light projected onto the road is decreased significantly.
So how can they be advertised as "Brighter" and "greater visibility"? Simple, because "brighter" is ambiguous and subjective, just like "louder" or "better". "greater visibility" is pretty much a lie no matter how its sliced, but its also subjective. Pure white light does have the advantage of improving contrast and, given the same light output, will improve visibility in clear conditions. The problem is that the bulbs with coating on them have a heavily reduced light output. I can guarantee that using a "Xenon" bulb will NOT make you see better, although maybe you will be convinced it has because you just spent money on them. As a warning, both true HID systems and these "blue bulbs" can both be referred to as "Xenon" -- but if it's an HID system, it'll require ballasts, and "blue bulbs" will not.
Also, the "before and after" shots that seem to "prove" how much brighter these new bulbs are should be ignored. Cameras can skew contrast and brightness very readily, and even the photos themselves can easily be manipulated to show the blue Xenon bulb as much brighter. In some of the shots you can even tell that the entire picture had been brightened because objects outside of the beam pattern are much brighter as well.
Another problem with the bluish color of the light is that it scatters more readily in poor visibility conditions. This is why some cars have (or used to have) yellow fog lights - the yellow is better illuminating through bad weather. The blue color is also more irritating to the human eye which is why true HID systems can be annoying to drivers. The natural yellowish tint of halogens is not as bad as its made out to be.
Also avoid all higher-wattage bulbs for obvious reasons - they put off more heat, they consume more power. Your car was not meant to use a 100 watt headlight bulb, and you might suffer electrical problems due to overcurrent or headlight housing issues because they put out so much heat.
You cannot put a HID retrofit kit into a car with halogen headlamps safely. For one, the halogen reflectors are not precise enough to control the HID light output and you'll be blinding other drivers, but also the HID bulb is a different shape than the regular one and the light is not going to be aimed correctly. The headlamp is a precise instrument and was designed with a single focal point, and if the bulb's filament or arc is not in the exact same position as the original one, the beam is going to be skewed. Some vehicles, especially those that came with HID systems as factory options, have entire headlight housings that can often be swapped into non-HID vehicle with minimal effort and will have the focusing characteristics appropriate for a HID bulb. At this point it would be safe and advantageous to use a true HID system.
The only thing I'd recommend doing to improve nighttime visibility with a halogen system is to get higher-efficiency bulbs such as Osram Silverstar (NOT Sylvania Silverstar), Sylvania Xtravision, Wagner BriteLite, and especially GE Nighthawk bulbs. These bulbs have clear glass and do not filter out any light, they simply have a more efficient filament that is more lumenous. The downside is that they probably won't last quite as long and they cost more (around $35-40 for a pair). For reference, a standard H3 halogen bulb puts out 1000 lumens on the low beam. a GE Nighthawk bulb puts out approximately 1150 lumens with the same power consumption. Not a huge increase, but still significant.
One other high-efficiency bulb that is difficult to find is something called "HIR" - halogen infrared reflecting. I've only seen these in 9005 and 9006 guises, and only a couple of times on eBay. You might be able to find them on Google. They work by reflecting the invisible infrared rays that all halogen bulbs produce back into the filament, making it burn brighter than a regular bulb. The seller claimed a huge improvement to lumenous properties with basically zero compromises. I have not personally tried these but I did find a review a while ago that favorably compared them to other non-HIR bulbs. The specs on them say that they produce almost 100% more light than a standard halogen! These are probably worth a shot, however they are pretty expensive for halogen bulbs ($60 for a pair).
It's easy to fall into the "Xenon" bulb trap because even reputable manufacturers make them. The Sylvania Silverstar is an example and is a ripoff (not only are they expensive, they put out less light than a standard halogen and also they only last for 150 hours instead of the standard 1000). Wagner TrueVision, LazerBlue, PIAA's stuff, and CoolBlue are all similar and should be avoided, unless having blue headlights and trying to look cool is worth driving blind at night.
So, in summary, here is some data to think about:
Standard 9006 halogen (low beam): 1000 lumens, 800 hour rated life $6
Sylvania 9006 Xtravision (low beam): 1060 lumens, 300 hour rated life $10
GE 9006 Nighthawk (low beam): 1150 lumens, 250 hour rated life $14
Toshiba HIR 9006 (low beam): 1800 lumens, 800 hour rated life $27
Sylvania 9006 Silverstar (low beam): 910 lumens, 150 hour rated life $20
If the glass on the bulb isn't clear, don't buy it.
Update, October 29, 2006: Sylvania has just released a new headlamp bulb, the "Sylvania Silverstar Ultra". I have not tried these yet but the general concensus among forum users seems positive. The specs on these new bulbs are decent: 1000 lumens (H3 low beam), 30% longer life than a regular Silverstar, and a 4000k color temperature. Be warned though that 30% longer than a regular Silverstar is still not very long and that these bulbs are expensive, retailing for about $50 for a pair, but fair weather visibility should be somewhat better than a regular halogen.
Update, November 05, 2007: I've finally been able to test the HIR bulbs for myself and the difference is obvious. The light output is still not as good as true HID systems but its definitely worth the money, and (in my opinion) a better value than HID. I definitely recommend HIR bulbs for anyone that can use them -- that is, if your car can utilize 9005 or 9006 bulbs. As far as I know, there aren't any HIR bulbs that work in dual-beam systems, yet.
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