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A glaring look at rear-view mirrors

Thursday, September 18, 2014

Some reflections on the challenge of looking backwards, followed by the vexing question: where, exactly, should video from a backup camera be displayed?

Mirror, mirror, above the dash, stop the glare and make it last! Okay, maybe I've been watching too many Netflix reruns of Bewitched. But mirror glare, typically caused by bright headlights, is a problem — and a dangerous one. It can create temporary blind spots on your retina, leaving you unable to see cars or pedestrians on the road around you.

Automotive manufacturers have offered solutions to this problem for decades. For instance, many car mirrors now employ electrochromism, which allows the mirror to dim automatically in response to headlights and other light sources. But when, exactly, did the first anti-glare mirrors come to market?

According to Wikipedia, the first manual-tilt day/night mirrors appeared in the 1930s. These mirrors typically use a prismatic, wedge-shaped design in which the rear surface (which is silvered) and the front surface (which is plain glass) are at angles to each other. In day view, you see light reflected off the silvered rear surface. But when you tilt the mirror to night view, you see light reflected off the unsilvered front surface, which, of course, has less glare.

Manual-tilt day/night mirrors may have debuted in the 30s, but they were still a novelty in the 50s. Witness this article from the September 1950 issue of Popular Science:



True to their name, manual-tilt mirrors require manual intervention: You have to take your hand off the wheel to adjust them, after you’ve been blinded by glare. Which is why, as early as 1958, Chrysler was demonstrating mirrors that could tilt automatically, as shown in this article from the October 1958 issue of Mechanix Illustrated:


Images: Modern Mechanix blog

Fast-forward to backup cameras
Electrochromic mirrors, which darken electronically, have done away with the need to tilt, either manually or automatically. But despite their sophistication, they still can't overcome the inherent drawbacks of rear-view mirrors, which provide only a partial view of the area behind the vehicle — a limitation that contributes to backover accidents, many of them involving small children. Which is why NHTSA has mandated the use of backup cameras by 2018 and why the last two QNX technology concept cars have shown how video from backup cameras can be integrated with other content in a digital instrument cluster.

Actually, this raises the question: just where should backup video be displayed? In the cluster, as demonstrated in our concept cars? Or in the head unit, the rear-view mirror, or a dedicated screen? The NHTSA ruling doesn’t mandate a specific device or location, which isn't surprising, as each has its own advantages and disadvantages.

Consider, for example, ease of use: Will drivers find one location more intuitive and less distracting than the alternatives? In all likelihood, the answer will vary from driver to driver and will depend on individual cognitive styles, driving habits, and vehicle design.

Another issue is speed of response. According to NHTSA’s ruling, any device displaying backup video must do so within 2.5 seconds of the car shifting into the reverse. Problem is, the ease of complying with this requirement depends on the device in question. For instance, NHTSA acknowledges that “in-mirror displays (which are only activated when the reverse gear is selected) may require additional warm-up time when compared to in-dash displays (which may be already in use for other purposes such as route navigation).”

At first blush, in-dash displays such as head units and digital clusters have the advantage here. But let’s remember that booting quickly can be a challenge for these systems because of their greater complexity — many offer a considerable amount of functionality. So imagine what happens when the driver turns the ignition key and almost immediately shifts into reverse. In that case, the cluster or head unit must boot up and display backup video within a handful of seconds. It's important, then, that system designers choose an OS that not only supports rich functionality, but also allows the system to start up and initialize applications in the least time possible.

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