Adaptive headlamps light up the night. Two other new driver aids are designed to help with night driving: adaptive headlamps and night vision. Both are optional; we found the first more useful than the second. The former uses a forward-looking light sensor behind the rearview mirror, but unlike the autronic eye automatic high-beam dimming feature in some late-1950s and 1960s American cars, it doesn't just switch between high- and low-beam. In the E-class, the high and low beams are in a single xenon fixture, which has a shutterlike device that continuously adjusts the cut-off. The unit is also able to move side-to-side to follow steering inputs. In practice, it continuously varies in steps between low and high beam and also adjusts the width and direction of the light pattern. It's pretty good at reacting both to the cars ahead and to oncoming traffic, but it's sometimes fooled by brightly reflective signs. On a dark, winding road with intermittent traffic, the system is pretty busy, which might drive some people nuts; and a driver who is paying attention could react faster to oncoming traffic, but overall the system is worthwhile because the beam pattern is so variable - you always get the maximum amount of light on the road. We were less enthralled with the night vision system, the latest version of a technology that first appeared on the current S-class (and which some other manufacturers offer as well). The enhanced pedestrian recognition works well - this would be great to have for driving through a busy subdivision on Halloween night - but, like all night vision systems, you really don't look at it much because you're looking out the windshield. Also, because it plays in the nav screen, you lose the navigation's map function.
Wake up! Or stop driving. On the subject of night driving, one of its greatest dangers is fatigue, and the E-class includes as standard the first-ever drowsy driver recognition and alert system. The system, which is active at speeds between 50 and 112 mph, monitors driver inputs. An alert driver makes more, smaller inputs, while a drowsy driver sort of zones out mentally for brief periods and therefore makes fewer inputs, but they're larger and more abrupt. Before judging the change in driver activity, the system spends the first 20 minutes establishing a baseline of the driver's style. The change in steering patterns is the most important indicator of drowsiness, but the software actually uses more than 70 profile elements - including the length of the drive and the time of day - in order to decide when to give the drowsy driver warning: a coffee cup symbol and "time for a break?" in the info display.