[SoCal]

This is for Randall, who can tolerate too-long posts. Everyone else probably will want to just skip ahead.

The question of what color, and how bright, the car instrument dials should be at night is a question of safety more than aesthetics.

The cones of our eyes don’t work as well in the dark as in daylight, and some colors are easier to see at night than others. In very dim light, we are most sensitive to green-yellow color. That's why you've perhaps noticed some European fire suits with horrid lime-green stripes. Even some fire trucks have switched from the traditional red to lime green.

But the question is more complicated than just the color in the spectrum, it also has to do with the brightness of that color. Red used to be the choice for night-vision goggles and HUDs, but the military has more recently switched over to green. But whether green is easier to see than red depends on the light intensity. The amount of illumination is a stronger deciding factor than the color itself.

Because our eyes are more sensitive to green, it is easier to see green at very low light levels than red. But the instument dials of the cars at night are not set for the dimmest light, but rather something brighter, so that there needn't be too much readjustment from looking through the dashboard as looking down at the instruments.

How bright to set the instrument dial is decided first, for that reason. The brighter the light, the more harsh effect on our vision and the longer it takes to get back to normal night vision.

Therefore, you don't want to have a light that is brighter than the intended purpose, including the relative adjustment the eye needs to make between looking through the windshield and looking down at the dials. If the light is brighter than it needs to be, and the wrong color, then the impact on our eyes is undesirable. Based on our relative sensitivity, a too-bright green light will be harsher than a too-bright red light.

Given the relative amount of illumination desired, a reddish light is usually preferred over a greenish light. Blue light is at the wrong end of the spectrum and is not optimal for dashboard illumination at night. White light also is not optimal, given the desired level of relative illumination.

So, a reddish-amber light is usually selected for night instrument illumination. At the desired level of illumination, it is easiest to see and least harsh on the eyes, and requires the least amount of adjustment when looking down at the dials and back up through the windshield.

But why did Porsche select amber? Probably because they thought it was pretty.