I've been reading up a lot on these aftermarket Halogens that we can buy but was disgruntled with the lack of a comparison between all the various ones you can buy. Most people tend to compare them with the stock headlights.
Anyway, I'll start this thread with my own comparison between two aftermarket halogens (that I have bought and used):
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1) Philips X-Treme Power +80% Halogens - $65
Marketed as: Up to 80% more light, 25m further beam, 30% whiter, ADR approved.
My findings: Probably more like 30-40% more light compared to stock. Definitely throws further down the road, slightly whiter when looking at the headlights itself.
The bulb itself has a blue tint just at the tip, which I suspect is what gives the light its slightly whiter appearance. Just a fraction (almost unnoticeable) whiter on the road.
City driving - not much different to stock or even the blue visions though you can see the beam cut-off much more easily with the X-treme powers (much like as if we have projector housings). In darker not-so-well-lighted up areas, you can really see how much more light these bulbs give out compared to STOCK and BLUEVISIONS. Things further down the road are much brighter and the spread also seems to be slightly wider.
The problem with having such a bright bulb is the lifespan of the bulb. X-treme powers, though they seem to provide one of the best amount of light output for halogen bulbs, do not last long at all.
My 2c: If you are looking for a LEGAL, brighter headlight replacements and don't care about the colour, this is for you.
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2) Philips BlueVision 4000k - $50
Marketed as: Whiter (4000k), brighter and ADR approved.
My Findings: Definitely whiter, a more ricey look - when looking at the headlights themselves. Doesn't seem any brighter at all in city areas compared to stock. Can't really see the beam cut-off in well lighted areas.
On the road, the light output is whiter, though to me it doesn't really make much of a difference in terms of perceiving or being able to see object more clearly. The X-treme powers in this regard are much better.
In not-so-well-lighted areas, the bluevisions give whiter light but the distance and power of the light itself is not much different to stock. Whiter probably gives a better perception of colour but that is about it (IMO).
The problem with blue-tinted (white output) halogens is the lifespan as well. The blue (or purple) coating changes the normal yellow output to white in colour, but in the process it decreases the amount of lumens (brightness). In order to compensate for the lack of brightness, manufacturers tweak the bulb to give more lumens, bringing the power back to normal standards whilst also providing white light. The whiter/bluer your light, the shorter the lifespan and the less lumens (power) you have.
My 2c: No real benefit other than looking nice
Did I mention it matches my white car well? 
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BlueVision vs. Xtreme Power FINAL SAY:
However, this said and done, you spend most of your driving in the city. Do you really need brighter or whiter globes? Personally it doesn't matter to me, brighter is always better but there isn't much difference in the city anyway. Might as well go with the whiter globes. If you are driving out in not so well lighted up areas - you'd use your highbeams for better vision anyway - wouldn't you? At that point, might be more worthwhile to change your highbeams to X-treme powers or similar instead if you are worried that the stocks aren't sufficient.
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Feel free to add your own reviews!
