UPDATE: I bought a set of LED lights off Amazon and it is like night and day! So much brighter. Fit great and I am very impressed.
They are the LASFIT H4 HB2 9003
6000K headlights....
I can only repost what I took time to write on nas-row.com:
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There's an issue of brightness temperature.
Most bulb manufacturers claim that the Sun is around 6000k, and we're used to that, so the bulb's brightness temperature should be as high as possible.
Now, bear with me for a while. Pardon me if you know all of this from the high school AP physics or elsewhere.
When/wherever there are particles scattering the light, light gets scattered, and depending on average size of the particles, different parts of the spectrum get scattered differently.
For instance, dust particles are much larger than visible light's wavelength, and the light experiences what is called Mie scattering. The fraction of light that gets scattered back doesn't depend on the wavelength and only depends on how large the particles are.
In fog, however, the water droplets are much smaller than the light wavelength, and this is termed Rayleigh scattering. The fraction of light that gets scattered (back and elsewhere) is proportional to the fourth power of the wavelength.
This is the cause of the sky to be blue, and this is the cause of the sun disk color temperature being actually lower (it does look yellowish, doesn't it?).
The ballpark wavelength of the blue color of visible spectrum is 450 nanometers, and the red - about 700. It means that in a fog, the most-reddish components of light will travel about 5.9 times further than blue. Curiously enough, red traffic light will appear red, yellow - somewhat reddish, and green - somewhat yellowish, which has been attributed to the initial choice of colors (that I have not been able to verify).
There are consequences to that:
(a) the light getting back to you from what you want to see on the road will also be scattered differently: the red-most components will propagate about 5.9 times further than blue-most. Between the losses back and fourth, it makes for an astonishing factor of 34 in difference in the amount of light you get back into your eyes.
(b) it gets worse: the glare back from the fog will be heavily biased towards blue part of the spectrum. So the bluer your lights are, the more heavily you are blinded by your own lights, and the less light you get from the objects on the road.
(c) the "other party" watching you from afar will also see more of the red light and less of blue light. It can be both a good thing and a bad thing.
That kind of leads to an obvious observation - that the "old-school" foglights were always amber, on the reddish side of yellow. As you may also know, in France for decades the headlights HAD TO be yellow. But the roads got better and this somehow faded away, and most of today's foglights are a fashion accessory.
To round it up:
LED lights are neither blue nor red, but on average their brightness temperature (and relative fraction of blue) is higher than halogens.
It makes no difference or makes it even better in dusty conditions (desert races), but it makes it a lot worse in fog.
Pick your poison.
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