In 2005, while visiting the International Autoshow here in Toronto, I checked the layout of the lights switch on some car models where a rotary knob was used. To my surprise, I found some solutions which did not satisfy the intuitive functionality I expected from these controls. Although seven years old, the design of these controls did not change dramatically lately (and not only them). Let me explain.
Firstly, trying to assess the mobility of our hands when working these type of knobs, imagine one grabs this knob, set to a vertical position, with his right hand (elbow next to the body). From here, comfortably, without moving the upper arm, the hand can turn only clockwise about 90 deg., but, with a bit of effort, it will go an additional 45 deg. angle both ways at the ends of the comfortable range. If the upper arm participates in this motion (stretching the arm forward, for example), then one would be able to turn that knob even more, adding almost 90 deg. to both clockwise and counter-clockwise turns (due to the mobility of the shoulder). The left hand has a similar, but symmetric range of motion. At this point, we can assume that, for a comfortable range, the left and right hands can turn such knob about 90 deg., from 12 o’clock position to 9 and 3 o’clock, respectively.
Secondly, it is my understanding that, visually, a vertical linear element represents or suggests activity (“active”, “on”, “engaged”, etc.), due to its perceived need of energy to keep this position, while a horizontal linear element suggests passivity (“passive”, “off”,
“disengaged”, etc.), since it resembles something at rest. You may think of someone standing vertically or resting horizontally.
Considering these two principles, and knowing that the light switch knob is operated with the left hand, I consider natural to have the “0” or “OFF” position at 9 o’clock and the “low beam” at 12 on the dial (“high beam” is not operated from here, but “parking lights” position would be within that range). In fact, the gradual increase of power follows the clockwise direction, satisfying another intuitive visual factor.
The results of my brief research show that, from 17 passenger cars, only one had its lights switch organized this way (from “9” to “12”), and that was a Pontiac. Other car manufacturers, including North American and European, had different types of switch layout. You can see all these examples below.
The longevity of this type of switch is given by a few important factors: reliability, easy access (without visual check), firm grip and continuous, gradual change of lights power. However, there might be times when not everyone can agree with this statement. What is your experience with these controls? Which one do you prefer?