Human eyes are more sensitive to blue light (maybe that's why in-dash high beam indicator lights is so darn irritating). This creates the illusion of greater light output; actually, the light is more dazzling, not brighter.
True, but careful, though: "more sensitive" can be a good thing, as when the output from a light source is rich in wavelengths near the peak of the Vλ or V'λ and thereby stimulating good visual acuit, or it can be a bad thing, as in the case of blue light stimulating a stronger glare reaction than non-blue light. The latter is the case with blue-tinted "whiter" headlight bulbs.
From oncoming traffic's perspective, the blue headlights appear to be brighter (see above), but from the driver's perspective, road/object illumination is poorer because blue-colored light is not brighter - it's just bluer.
I agree. There's a big gap between the (small) amount of light it takes to cause or worsen glare, and the (large) amount of light it takes to light up objects on the road effectively for the driver, who really needs all the light he or she can safely get.
Philips offer an intriguing alternative for those who simply must have more color in their life - Philips NightGuide. This bulb is purported to increase safety by adding a little color to the fringes (only) of beam patterns by adding rings of different colors toward the base of the bulb.
Yeah, supposedly a blue patch along the curb side of the beam and a yellow patch near oncoming drivers' eyes. It's an interesting trick, but pointless and silly (in my opinion) for a few reasons. For one thing, this is not 1982, when all replaceable-bulb headlamps used parabolic reflectors and formulaic optic configurations. Now, there's an enormous variety of different optical techniques even if we just look at headlamps that take one particular kind of bulb. So the blue and yellow filter patches on the bulb don't necessarily put the blue and yellow patches at any particular place in the beam pattern. Philips attempts to get around this by marketing "H7R" and "H7S" for reflector and projector headlamps, respectively, but...sheesh. The only reason I don't rant harder at this silliness is because as gimmicky bulbs go, these are relatively benign and the rest of Philips' line contains really good, high-performing options without gimmicks.
If the bulbs are blued - you're screwed.
+0.75. I can't quite say "+1" because there's an interesting exception to this otherwise sound rule of thumb: the blue ring near the tip of bulbs like Xtreme Power, Xtreme Vision, and GE Night Hawk Platinum. The marketers say this is there to make a fashion statement with your headlamps. And from various off-axis angles as you observe the headlamp, you do see some blue. But that's not the actual reason it's there. It's really there to cut the mean spherical output of the bulb down to legal levels as tested in an integrating sphere. Clever trick: filter a part of the bulb that has nothing to do with beam formation because it's located where the reflector isn't looking for the filament. Give the kids a blue flash they can point to from certain angles without coloring the beam or filtering out any usable light. Meanwhile, the filament is pumping mad lumenzz through the uncolored glass where the reflector is looking.
One "exception" to the above rule to ponder: yellow tint in fog lights have been most helpful to me when driving in snow or severe weather. They offer a color contrast that complements the white headlights. Another benefit - cosmetic - is you don't have to worry about color temperature matching foggies to headlights - they just look cool. Light output in foglamps, although important, takes a (slightly) back seat to beam pattern (flat & wide) and source location (the lower the better).
I agree with all of this. Stern's got a
pretty lengthy article on yellow light for fog lamps, including a discussion of the filtration losses (which are trivial with yellow, compared to large losses with blue).
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