If you’re like me, you’ve been staring agape at the ’s ominously vengeful face since last week. And you might’ve also noticed that the truck has five little lights on its roof. These lights serve a specific purpose: they’re a government-mandated mark of shame for vehicles that are so huge.

I’ve emerged from a deep research rabbit hole and boy, there sure are a lot of rules regarding the size, quantity and location of lights mounted on a vehicle. The lays it all out in exhaustingly specific English, and of course we’re all familiar with of the Electronic Code of Federal Regulations.

Don’t click either of those links unless you want to spend the rest of your day lost in a riveting tale of optical optimization!

First of all, yeah, no, on your Christmas list is probably illegal and it’s definitely obnoxious. If you must install one, use it off-road and that will be the end of it. If you leave it lit on the highway, we will find you, and it will be very bad for you.

Just kidding. We could explore the nuances of lighting law all day, but we’re here now to learn about the little five-lamp tiara that’s often seen across the roof of some pickup trucks and all big rigs.

Those lights are part of the truck’s conspicuity program. Cool word, right? It just means that the lights exist so the truck can be seen; they’re not meant to help the driver’s vision like spotlights or the aforementioned LED bars.

If a vehicle is 2,032mm (80 inches) wide or wider, it has to have three little lamps mounted “as high as practicable” to indicate there’s a Big Ol’Boy coming through. These are called Front Identification Lamps (and actually describes their purpose as simply to “indicate presence of a wide vehicle.”)

Something with that much girth also has to have at least two Front Clearance Lamps, outboard of the Front Identification Lamps, to indicate basically how wide the vehicle actually is.

At this point it’s important to note how overall vehicle width is actually defined by the U.S. government, and why some trucks need these little lights and others don’t:

...nominal design dimension of the widest part of the vehicle, exclusive of signal lamps, marker lamps, outside rearview mirrors, flexible fender extensions, mud flaps, and outside door handles determined with doors and windows closed, and the wheels in the straight-ahead position. Running boards may also be excluded from the determination of overall width if they do not extend beyond the width as determined by the other items excluded by this definition.

So mirrors and fender flares don’t count. That’s why some large looking pickup trucks and the Rolls-Royce Cullinan get to be enormous without having to wear the “wide load” lights.

For vehicles that do need them, these lights are generally mounted high up so oncoming vehicles can see them from far away. Imagine if you’re coming over a rise—spot those helpful front identification lamps, and you can be all “oh man, big truck coming, I better get excited!”

Yeah, there’s not much you need to do when a truck is coming towards you in the other lane. But it can be helpful if you see these lights in your rearview mirror; you’ll know you’re about to be passed by wide vehicle.

Another practical use of these Clearance and Identification lights could be while a truck is maneuvering near a loading dock-like area. In that scenario, the lights would help spotters see if the truck was going to fit through an opening or whatever. These also help outside observers see the truck’s general outline for overhead clearance, which is a concern with big rigs.

The Ford Raptor, a truck with no business anywhere near a loading dock, famously has Identification lamps in the top of its grill and clearance lamps at the edges of its massive fenders. (The Raptor is a comically massive 86.3 inches wide.)

In this case the lights are mounted lower. Legally speaking, they need to be mounted “ as high as practicable” but the government doesn’t specify that they must be on the roof per se. Obviously, sanctioning bodies are OK with Ford’s interpretation here because the raptor has had the lights in the grill since the first generation came out almost a decade ago. Now the little three-amber-light constellation that has become an element of the Raptor’s iconic smile.

Even more recently, I’ve noticed people putting Raptor-style grill lights on Toyotas. Looks pretty cool. But be warned: there is a chance a disgruntled cop could get you into trouble over “misrepresenting the size of your vehicle” by having these lights on a vehicle that is under 80 inches wide.

That’s just I saw, I can’t find any actual laws against little aftermarket amber lights. But I figured I’d pass the info along all the same.

If you insisted on scrolling right past all my jaunty prose, here’s the TL;DR:

Vehicles 80 inches wide and wider need five extra lights.

Three of those lights are in a row in the middle to indicate the presence of a wide vehicle...

One of those lights sits at each side, at the widest point, to indicate how wide the vehicle is specifically.

Anyway, now you know what the deal is with those five little lights decorating the tops of some pickups and big rigs. Don’t forget to regale your friends with this incredible knowledge every time you see a truck.