Briefly:
- I frequently have a hard time seeing stop lights, if I’m first in line, due to the steeply sloped windshield of the Prius Prime.
- This is, apparently, a fairly common problem on modern cars. Good aerodynamics require a sleek, low-profile shape.
- The common solution is to crane your neck as required, and get on with life.
- There are devices that address this problem, but I find them lacking. They are either antique designs, finicky, provide barely-usable images, permanently intrude on field of vision, or all of the above.
- I’ve come up with my own solution, but I’m waiting for the parts from Amazon. I’m going to try a visor-mounted flip-down cheap Fresnel lens. Total cost, including zip ties to attach it, about $3. Alternatively, I’ll need to buy a “wide angle Fresnel lens”, which will likely cost around $10, but will give me an upright image.
- I believe there’s so little potential profit in this that I’m putting the design in the public domain.
1: The obvious brute-force solution.
The inability to see an overhead traffic light is a long-standing problem for U.S. drivers. And by long-standing I mean that we are merely the most recent of a century’s worth of neck-craners. The earliest patents for devices addressing this issue date to the 1920s.
Here and now, in 2022, I have to start by acknowledging the obvious brute-force solution: Use a dashcam. High-quality live cameras are cheap and ubiquitous. You want a clear picture of the traffic light in front of you, obscured by your low-slope roof? Buy a $30 dashcam, mount it tilted up a bit, and glance over at the picture, as required, to see the traffic light. Clear image, zero ambiguity, problem solved. I haven’t actually tried this, but I have a hard time seeing what could go wrong. These things have high enough resolution to let you read license plate numbers on the cars ahead of you. I’m sure you’d be able to distinguish red/yellow/green on a traffic light.
Source: Amazon.
In the modern world, if you want to see something that’s not in your line of sight, just point a camera at it. Problem solved.
(If nothing else, you could just use your phone. Turn on the rear camera, point it at the light, look at the screen. For a variety of reasons, I’m assuming that’s not a desirable or practical solution.)
But, seriously, where’s the fun in solving this problem with a camera. If your kid wants a pet, would your first thought be to buy a robot dog? Would you turn your back on a century’s worth of marginally-functional Rube Goldberg devices, just because a camera would actually solve your problem?
Plus, there are some downsides to a dashcam. The type with attached viewing screen permanently obscures part of your field of view. You have to deal with the power wires, one way or the other (either permanently wire it in, or have a power wire dangling from your cigarette lighter socket). If you cause a crash, your own camera will have recorded incriminating evidence. And in the end, it’s just so much landfill fodder: Cheap electronics, baking in the sun on your dashboard — how long do you really expect that to last?
In the rest of this post, I’m going to look at what I term optico-mechanical solutions. Little bits of glass or plastic, strategically placed to give you some indication of what the traffic light over your head is doing.
2: Prior art and current offerings.
This Google Patents entry has a nice listing of prior patents on “signal-viewing devices”, dating back to 1927.
The first such patented device was half a magnifying glass (“plano-sperical lens), glued to the windshield with clear cement. As shown below. Presumably, you’d see a little upside-down image of whatever was in front of you, in that lens. Thus enabling you to tell when the light had turned green. Fedora optional.
Source: Google Patents.
The next iteration mounted the magnifying glass outside the car, attached to the exterior sun visor. Still with optional fedora.
Source: Google Patents.
A 1936 variant used something more complex than a fixed magnifying lens. This incorporates a long, thin lens backed by a mirror, roughly the same size and shape as a standard rear-view mirror. I honestly could not quite grasp how it worked. The only thing that was clear was that it was designed so that the driver could adjust the angle, using the same ball-and-socket connection as you would find in any rear-view mirror.
Source: Google Patents.
In 1951, the classic “prism” signal viewer was patented, circled in red below. This one doesn’t have any sort of perfect lens, so it doesn’t attempt to provide a clear, undistorted picture. Instead, it’s more a chunk of glass or plastic that can provide some indication of color of the lights overhead. This type of signal viewer is still in production — you can pick up a modern copy for about $10. So, presumably, it must have worked fairly well. But, by reputation, you can’t easily distinguish (e.g.) left-turn arrows. Thus it appears more suited to a simpler era, with simpler stop lights. Still with a fedora.
Source: Google Patents.
Source: Amazon.
As a variation on that, you could purchase a more polished and elegant version of the classic prism. This is clearly designed to be permanently mounted at some point on the dashboard of the car.
Source: Amazon.
By the 1970s, we had cheap plastic fresnel lenses. These provide their focusing via a series of concentric “steps” cut or molded into a sheet of plastic or glass. With this invention, you can cheaply provide quite large lenses that can easily be stuck to glass. This 1971 patent suggested using them to let the driver seen into what would otherwise be blind spots around the car. I will note in passing that a Fresnel lens provides a much rougher image than a classical, full-thickness lens. But apparently a rough image was adequate for this purpose.
Source: Google Patents.
A 1981 patent was just another magnifying glass mounted on the windshield. This time, with an adjustable mounting so that, presumably, the driver could orient it as needed.
Source: Google Patents.
By the mid-1990s, somebody hit on the idea of attaching something directly to the now-ubiquitous internal sun visor. In this case, the patent is just for some viewing ports or peep holes cut into the sun visor.
Source: Google Patents.
This next one improved that peep-hole concept by moderating the amount of light passing through the sun visor. As with the patent above, it lets the driver see the traffic light, even if the sun visor is down. In this case, the device consists of two polarized lenses, so that the driver can see through the visor, but adjust the amount of light that passes through.
Source: Google Patents.
I’ll note that the era of cheap plastics has made all of the various peephole-style sun visors obsolete. In the modern era, if you want to see through your sun visor, you just replace the opaque sun visor with some sort of tinted plastic. These are generally termed “car visor extenders”, and attach to the existing sun visor with clamps or straps. Some swing into place, some slide into place, but the basic idea is always a sheet of tinted plastic in place of the opaque visor.
Source: Amazon, Google Shopping
Finally, in 1998, somebody came up with the idea of sticking a vinyl Fresnel lens to the top of the windshield. This is one of those cling-type lenses that is applied by wetting it, and can be peeled off. This one is also still in production, and you can buy a copy for about $23.
Source: Google Patents.
Source: Amazon.
3: Proposed solution, awaiting parts from Amazon.
First, let me list a few constraints, in my situation.
a) Not hand-held. For sure, you could just leave a sturdy (e.g., metal) mirror on the dash, and hold it so that you could see the traffic lights as required. But juggling objects as you drive is just a bad idea.
b) Not permanently in the field of view. The Prius already has limited visbility, with broad A-pillars, the steeply sloped windshield and roof, and so on. I find myself trying to peer around the rear-view mirror when making turns. I don’t need anything else obscuring my field of vision as I drive.
c) Not permanently mounted. This is my wife’s car, and I’m not going to be (allowed to) go around drilling, gluing, and so on.
d) Adjustable. I imagine I’ll need to use this at various angles, depending on the traffic light in question.
What I propose is a hybrid of two devices above.
Take the practicality of a broad Fresnel lens (this got lots of positive reviews on Amazon):
But instead of mounting it permanently to the windshield, give it the cheapest possible mount to the sun visor, so that I can flip it down only when I need it:
So, take the picture above, replace the plain green sheet with a clear Fresnel lens, replace the straps with zip ties, and mount it “the other way around” to that it can be deployed while the visor is flat against the roof.
The cheapest solution here would be to order a large, cheap magnifying Fresnel lens from Amazon. Those are rigid and could be directly attached to the visor. But, upon reflection, I don’t think my brain can reliably handle the upside-down and side-flipped image those would produce. Around here, its not a question of facing a (one) traffic light, it’s a question of facing a string of them, across multiple lanes. Looking at a side-to-side reversed imaging, for a complex set of stop lights, is just begging to have an accident.
A better but more expensive solution is to buy a “wide angle” (i.e., negative-focal-length) Fresnel lens. With that, I’ll get the image right-side-up, instead of upside-down. As shown in the `1974 patent above, these were first conceived of as blind-spot avoidance devices. And that’s exactly how they are used today. These are still widely available, as in this $10 model from Amazon. Unfortunately, all the ones I see for sale are floppy, and would require some sort of clear sheet as a backer if used in this application.
I guess I’ll order one of those, and maybe a cheap sun visor extender, and see how that turns out. I’ll report back when the materials arrive from Amazon.
And if that fails, I guess I can always buy a dashcam. And a fedora.
