Why do yellow fog lamps work better?

why do yellow fog lamps work better? It's because of the way the human eye interacts with different colors of light. Blue and violet are very difficult for the human optical system to process correctly. They are the shortest visible wavelengths and tend to focus in front of our eyes' retinae, rather than upon it. To demonstrate this to yourself, find a dark blue store front sign or something else that's a dark, pure blue against a dark background in the absence of white light. From any appreciable distance, it's almost impossible for your eyes to see the blue lighted object as a sharply defined form...the edges blur significantly.) Blue also is a very difficult color of light to look at if it is at all intense...it stimulates the reaction we call "glare". So, culling the blue out of the spectrum lightens the optical workload and reduces glare.

My understanding is that it is important for fog lights to be one color (rather than white, which is all colors) because the different wavelengths(colors) of visible light scatter off the fog droplets differently. This phenomenon is known as "dispersion," because the different colors of light in an image will separate from each other, causing the image to "disperse." If you illuminate the road with only one wavelength (color) of light, the images of the objects you see will still become somewhat blurry because of the scattering of light by the fog, but at least you won't have extra problems from dispersion. So, if we want to use just one wavelength of light, which wavelength should we use? It turns out that light with short wavelengths scatters more than light with long wavelengths (short to long: violet, indigo, blue, green, yellow, orange, red). So, a long wavelength light will be best. There's another thing to consider, too: our eyes are not equally sensitive to all colors. It turns out that we are most sensitive to yellow and green light. So, our best compromise between sensitivity for our eyes and a long wavelength for least scattering is yellow light.

Now, everybody doesn't know what kind of light bulbs are used in fog lights, but another consideration used in street lighting is cost and efficiency. You may have seen some yellow street lighting in some places; this is "low-pressure sodium vapor" lighting.

The special thing about this light is that it is almost entirely one (actually two very close together) wavelength of yellow light, and that it gives the most illumination for the amount of electricity. A big problem with this light, though, is that it throws off color perception. Under sodium vapor light, something blue looks gray. This makes it hard to, say, recognize your car in a parking lot.

Good (and legal) fog lamps produce white or Selective Yellow light, and use tungsten-halogen bulbs. Xenon or HID bulbs are inherently unsuitable for use in fog lamps, and blue or other-colored lights are also the wrong choice.

What are Fog Lamps Really For?

The fog lamps' job is to show you the edges of the road, the lane markings, and the immediate foreground. When used in combination with the headlamps, good fog lamps weight the overall beam pattern towards the foreground so that even though there may be a relatively high level of upward stray light from the headlamps causing glareback from the fog or falling rain or snow, there will be more foreground light than usual without a corresponding increase in upward stray light, giving back some of the vision you lose to precipitation.

When used without headlamps in conditions of extremely poor visibility due to snow, fog or heavy rain, good fog lamps light the foreground and the road edges only, so you can see your way safely at reduced speeds.

In clear conditions, more foreground light is not a good thing, it's a bad thing. Some foreground light is necessary so you can use your peripheral vision to see where you are relative to the road edges, the lane markings and that pothole 10 feet in front of your left wheels. But foreground light is far less safety-critical than light cast well down the road into the distance, because at any significant speed (much above 30 mph), what's in the foreground is too close for you to do much about. If you increase the foreground light, your pupils react to the bright, wide pool of light by constricting, which in turn substantially reduces your distance vision—especially since there's no increase in down-the-road distance light to go along with the increased foreground light. It's insidious, because high levels of foreground light give the illusion, the subjective impression, of comfort and security and "good lighting".

VVT-i = Variable Valve Timing with intelligence

VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota. The Toyota VVT-i system replaces the Toyota VVT offered starting in 1991 on the 4A-GE 20-Valve engine. The VVT system is a 2-stage hydraulically controlled cam phasing system.

TOYOTA’s Variable Valve Timing with Intelligence engines use advanced computer technology to vary air intake according to driving conditions and engine load. By adjusting the overlap time between the exhaust valve closing and intake valve opening the engine can be tuned to provide instant engine torque across the entire rev range.

VVT-i brings substantial advantages in 3 main areas:
# It allows sporty performance.
# Reduces your petrol costs.
# More complete fuel burn at higher temperatures leads to fewer harmful emissions.

VVT-i, introduced in 1996, varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt, scissor-gear or chain) and intake camshaft. Engine oil pressure is applied to an actuator to adjust the camshaft position. In 1998, "Dual" VVT-i (adjusts both intake and exhaust camshafts) was first introduced in the RS200 Altezza's 3S-GE engine. Dual VVT-i is also found in Toyota's new generation V6 engine, the 3.5L 2GR-FE V6. This engine can be found in the AVALON, RAV-4, and CAMRY in the US, the AURION in Australia, and various models in Japan, including the ESTIMA. Other Dual VVT-i engines include the upcoming 1.8L 2ZR-FE I4, which will see implementation in TOYOTA's next generation of compact vehicles. By adjusting the valve timing, engine start and stop occur virtually unnoticeable at minimum compression, and fast heating of the catalytic converter to its light-off temperature is possible, thereby reducing HC emissions considerably.

High Intensity Discharge ( H I D ) lights.

Fifteen years ago, lighting technology took a leap forward with the invention of “High-Intensity Discharge” (HID) automotive headlights. They first appeared on the 1991 BMW 7 Series. Today, as costs decrease, HID Headlights are becoming available on at least some models from the nearly every major manufacturer.

Description:
# High Intensity Discharge (HID) lights, also know as Xenon lights, produce a bright light resulting from an electric arc inside a capsule full of Xenon gas. Many times, HID lighting appears to give off a bluish tint when the bulbs are lit. This technology produces a significantly brighter and whiter light than that of a standard halogen light. HID lights first began appearing on luxury cars in the late 1990s and are becoming increasingly more common as standard equipment.
# The automotive HID (high intensity discharge) headlight lamps are often referred to as xenon lamps but they are more of a specialized metal halide lamp than anything else.
# Once illuminated, HID light output is three times that of halogen, and as an added benefit, the ignited gas uses very low voltage, thereby reducing the load on the alternator. The light, now at a “hotter” color temperature than halogen, appears nearly white. The powerful white light makes distant street reflectors and signs highly visible to the driver. As HID light is more intense, the bulbs are typically placed behind projector beam headlight assemblies. These lenses allow the bright HID beam to be very focused, often with a very pronounced beam cut-off, or area where the light stops, to reduce glare to opposing traffic. In addition, most HID-equipped vehicles have standard beam leveling control, dropping and raising according to vehicle load and angle, to further prevent glare to other road users.
# Early HID headlights were only used for the low beam, with a halogen bulb reserved for high beam use. As reflector technology has improved, “bi-xenon” headlights (offering both a “low” and “high” HID beam) are offered on many vehicles today.

Purpose:
# As a newer headlight technology, HID lights provide better visibility at night, which help to improve nighttime driving safety.
# HID lights also consume less electricity than their halogen counterparts, reducing load on the car’s electrical system. Because of the projector-like technology of HIDs, their high-tech appearance is also a welcome addition to today’s vehicle designs.
# HID lamps produce up to 70% more light than standard halogen bulbs, and have a longer service life than conventional sealed beams or halogen lamps,

Maintenance Tips/Suggestions:
# They also last longer. With an expected lifespan of 3,000 hours (about 90,000 miles for the average driver), many consider HID headlights a “lifetime” bulb that never needs to be replaced. Even if the bulb does burn out (and they can), the modular design allows bulb-only replacement, much like traditional headlight bulbs.
# Check headlight operation frequently and always replace defective bulbs with another of the same exact type. During replacement, be careful not to touch the bulb itself as the oil from your skin can cause the bulb to fail.
# Cars with HID lights from the factory meet lighting safety requirements for that specific make, year and model. If you plan to retrofit your car’s standard halogen lights over to HID, make sure the bulbs/conversion kits result in a legal installation for street use.
# HID conversions are usually more involved than just a simple bulb replacement and require thorough research before making the decision to switch.
# Many active safety features are invaluable as driver aids but rarely used. HID headlight is an active safety feature that is used frequently, increases headlight reliability, and improves driver visibility.