I have been trying to upgrade the lighting on my S70 and doing a lot of digging on the net, and thought others might like to see my notes on this topic as well. There is a great deal of disinformation out there...

HID bulbs should not be simply retrofitted into stock halogen lamp housings. Even if you get a wiring kit with ballasts, the output pattern is very different than with halogen bulbs, so not only do you need a change of wiring, you need to have a change of lamp housing (reflector and lens) to properly use HID bulbs. Otherwise your results may be poor visibility, and/or dangerous to oncoming drivers.

The rest of these notes are all about standard H7/55W S70 bulbs, which use a halogen gas and a tungsten filament...
[ul][*]The H7/55 specification specifies not only the plug configuration and power consumption (55 Watts), it also specifies the total lamp output (1450 lumens)[*]Actual sample bulb output is permitted to vary +/- 15% by the specification[*]This means, that for bulbs meeting the legal specification, the brightest can only have 30% more total output than the dimmest, period. There is a lot of marketing talk and misconception that distort this basic fact. It is simply not possible to have an H7 lamp with double the output of the garden variety H7 lamp.[*]So permitted total output variation does have a 30% range[*]Some claims of e.g., 50%, 80% increase in light may be valid, but what this means (if it's true at all) is not 80% more total light, it means 80% more intensity measured at a particular location. if this sounds confusing, consider that:
[ul][*]light intensity doesn't need to be uniform in all directions, i.e., there may be "hot spots"[*]even if it's uniform, the beam can be more tightly focused for bright light in a small area, or less tightly focused, for dimmer light over a large area[/ul][*]Halogen bulbs use a tungsten filament
[ul][*]filament life is an importantconsideration[*]the hotter it's run, the brighter it will be, but normally the shorter its life will be[*]no matter what the manufacturer does to differentiate their product, final total output must be 1450 lumens, +/- 15%[*]the visible output of the filament is mostly in the red-orange-yellow-green bands of the visible spectrum[*]there is relatively little output in the blue-violet visible bands (perhaps 15%)[/ul][*]It's become popular to use glass that passes primarily blue-violet in some modern halogen bulbs. This is done principally for fashion, as the output color can mimic HID output color (but they can't reproduce the intensity). Even withinstandard H7-halogen designsconsider the downsides of these bulbs, which can be very expensive.
[ul][*]If you filter the filament output, you are throwing away light - there is no getting around that[*]Because about 85% of the output is not blue or violet, filtering to make it principally blue-violet is *very* inefficient[*]The bulb will either be dimmer, or if it is run hotter to increase output to make up for the filtering, it will have a shorter lifespan[*]It may even be dimmer *and* have a shorter lifespan[/ul][*]When it comes to the "color" of the output, assuming it's not neutral white:
[ul][*]red-shifting the output (warm/yellowish light) tends to be easy on the eyes, produce low glare and fatigue[*]blue-shifting the output (cool/bluish light) tends to increase visual acuity, but also increases glare and fatigue[/ul][*]In addition to placing total outputnear the upper end of the allowed specification range (1450+15%=1667 lumens), a manufacturer may use a tighter focused beam to give visiblity at a longer distance.
[ul][*]Of course, if the output is the same, and you focus tighter, you get more usable distance, but less breadth of light, i.e., less light at the road's shoulders[*]One way to do this is to reduce the size of the filament or the filament as well as its quartz envelope[/ul][*]The most widely respected brands available here in the US are GE & Philips
[ul][*]GE has their Nighthawk bulbs, claim 30% increased output[*]Philips has (of interest to me, and I couldn't care less about 'style', I want lighting function)
[ul][*]X-treme Power (claim 80% increased output)[*]VisionPlus (claim 50% increased output, and 15-20meters greater distance)[*]NightGuide (like VisionPlus, but have a novel 3-color spatial pattern, cool-blue at right to read signs, pure white in center, and warm yellow at left to decrease fatigue, reduce hazards to oncoming drivers)[/ul][*]PIAA seems to make some gimmicky yet expensive bulbs, some of which perform quite poorly in independent testing[/ul][/ul]

Hope others find these notes useful!

 

For those interested... here is a plot showingof the spectral output of sunlight (red curve), as well as a tungsten halogen lamp (black curve), disregard the 2 other traces. Two things to note are:
[ul][*]Compared to sunlight, the halogen output is equally broad, but it is shifted to the red[*]One can clearly see that the halogen output is low in the blue and violet bands (reference either the wavelength axis or the corresponding spectral colors shown below)[/ul]

 

It is widely known that you can blind people with HID's in your stock housings. However you can still do this and it will look fine. A realignment of the lights should be the key to helping with this.

 

Ok, here is a juxtaposition of some comparison photos of bulbs of interest that I made from some photos I found on this German site here:
http://www.tspaeth.de/fuers-auto/sho...nt.php?coID=10

The photos were taken by a professional photographer with the camera set on manual exposure, and identical shutter speed and aperature, so the differences are not due to the camera adjusting - it's exposure parameters are all the same.

I have cut out a key region for each that shows the lighting in the distance for 4 bulbs of interest, labeled themand juxtaposed them adjacent for visual comparison... interestingly, even the $20 Philips VisionPlus beats the $75 PIAA X-treme White, and they are arranged in the order I think is worst to best.In my opinionthe Philips X-treme Power is the brightest, but the Philips NightGuide (longer life) is close behind, and perhaps showing a bit better contrast in the violet region. At this point I am thinking of using the Philips X-treme for the high beams and the Philips NightGuide for the low beams (longer life for the daytime running use).


[IMG]local://upfiles/13385/A3E2E42F4243499188A6F03A2A9EEABD.jpg[/IMG]

 

1. Where the bulbs placed in the same exact car?

2. If so where they realigned after each switch to the same exact specs as the first one?

 

My understanding is yes to both. They were trying to make this as close a correspondence as possible so as to isolate the observed variation as being due to the bulb performance. I believe they've done that quite well, because the 3 Philips products compare just as they should based on their product designs, as well as several independent tests I've read on them and those PIAAs. This comparison image is a nice visual summary though.

 

ALL HID's

HID Low Beams in OEM Reflector Housing


50w 4300k reflector housing


35w 5000k Reflector Housing


35w 5000k Low Beam Reflector Housing


35w Low Beam Reflector Housing

 

If there isn't a serious effort made to reproduce exposure conditions, it's not possible to compare separate images... I see that on the GE website, where they show comparison images involving their Nighthawk bulbs. I can't prove it, but I think the apparent improvements are primarily due to exposure differences.

Likewise, in my opinion at least, you need to look at what is lit by the lamps, not the lamps themselves, for best understanding of lighting performance.