Whiteness

Whiteness, associated with color temperature, is the color appearance of a light, measured in degrees Kelvin (K). Natural daylight at noon has a color temperature of 4870K. High performance halogen , such as SYLVANIA SilverStar, has a color temperature of approximately 4000K, comparable to high intensity discharge (HID), which is 4100K.

In contrast, standard halogen headlights are only about 3200K and have a more yellow appearance.  The two ends to the specific spectrum are yellow and blue, the higher the color temperature, the closer to blue.  This is why lights that are high in color, such as HID and SilverStar, are percieved as blue, they are actually just less yellow. 

Below you will see the whole spectrum including white for headlights, amber, reb, blue and green.  A vehicles signal, a road construction blinker, the yellow (amber) of stop lights are amber.  Red is for brake lights, the red in stop lights and emergency vehicle  such as police, fire and ambulances.  Blue is reserved for police and emergency vehicles.  Green is mainly for traffic lights.  

Brightness

Brightness, associated with luminance, is the amount of light reflected in a particular direction. High performance halogen headlights, such as SYLVANIA SilverStar® and XtraVision®, have greater luminance than standard halogen headlights and direct more light on the road. 

Luminance is different from lumen (the basic measure of light output).  The definition of luminance is the amount of visible light on a point on a surface in a given direction or increased light in the most important spots on the road while driving.  Higher Luminance is achieved through increased control of the filament and, overall, control of the light coming off of the filament.  Light output (lumens) isn't increased but the light is made more useful.