Strobe effect on Cadillac brake lights?

In the past couple of years, I’ve noticed that the rear brake lights on Cadillacs (and no other makes of car) almost have a very rapid strobe-light effect. When I stare at the lights and then shift my eyes ever so slightly, it is very noticeable. Has anybody else noticed this?

LED’s. Pulsed output.

I’ve noticed this too. The Cadillacs and other newer cars you’re seeing use light-emitting diode (LED) tail/brake lights instead of standard incandescent bulbs. To control the brightness of the tail/brake lights (dim when acting as a tail light, but bright when braking), the LEDs must be switched on and off at somewhat-high frequency. This pulsing (pulse-width modulation, I think) causes the flicker you see.

Some people seem to be more sensitive to this than others. To me, it’s distracting, and I wish they’d just light fewer LEDs for the tail light, rather than dimming all the LEDs in the array. I do like LEDs as brake lights in principle, since they come on instantly, and are more noticeable.

I’ve always run brake light flashers on my motorcycles (Hyper-Lites is the brand name). It’s anecdotal, I know, but I’m pretty sure they’ve saved my ass a couple of times.

Yes, PWM was mentioned, it is a common technique to control the brightness of LEDs. I’m very sensitive to the flicker and I’ve come across many “cool and advanced” architectural lighting schemes that I can notice the flicker (despite claims of it being imperceptible) and often develop a headache from it. Peripheral vision is especially noticeable, which is why it really stands out with automobile applications.

It’s unfortunately reminding me of the CRT refresh rate days and I’d thought I’d been able to say goodbye to those monitor-flicker-induced headaches :frowning:

This has been bugging me more and more. The lights themselves have always bugged me, but the fact that Cadillac hasn’t fixed it is just inexcusable. Lots of cars nowadays have LED tail lights, and the only ones I see that flicker like this are Cadillacs. Recently I saw a new giant Cadillac SUV that has its tail lights going all the way up on either side of the rear window, so they’re huge, and they’re still making them so they flicker.

The strobing is fast enough so that I can’t see it if staring directly at the light, but when my eyes are scanning around (which they are constantly doing), the flickering appears as extra tail lights all over the place, and it’s very distracting.

Is there someone we can complain to about it? I think it’s a safety issue.

I’ve seen plenty of cars where the taillights flicker, it’s not just Cadillac. I don’t see how it’s a “safety issue” which needs to be “fixed.” And it’s not just as simple as increasing the PWM drive frequency, since blasting (relatively) high current square waves over a wire is a good recipe for EMI problems.

If the flicker rate is between 3-30 hertz (flashes per second), it can trigger a seizure (photosensitive epilepsy).

I think it’s a (small) safety issue because it’s distracting - I find myself looking around to find the ghost image that appeared in the wrong place.

Have you seen other cars that do it? For the last year or two, I’ve been making a point to notice, and every tail light that I see flickering turns out to be a Cadillac.

Sure, simply increasing the PWM drive frequency could increase the chance for electromagnetic interference, but why can’t Cadillac solve the problem like every other car maker seems to do? I don’t know what they do differently, but other cars don’t have this problem.


I’ve noticed this on a great many cars, certainly not just Cadillacs. I’ve also noticed it in many other places. I’ve seen this, for example, on those tall radio broadcasting towers with the blinking red lights on them – I get that strobe effect from them too.

The Exploratorium in San Francisco has had a display of this effect, that has been there for at least the last 30 years or so. If you look straight at it, you see a large collection of little lights, in the pattern of a large script letter “I” (that’s a Capital Eye letter). If you move your eyes just slightly (which of course you do a lot), or see the display in your peripheral vision while your eyes are moving around, you intermittently see the word “eye” written in script, or you see a pattern of an actual eyeball.

I found it very disturbing to look at, until I understood what was actually going on.

I’ll poke around and see if I can find a picture of it on-line somewhere.

Sorry, I found a zillion pics of Exploratorium exhibits, but not this one.

Here seems to be a really brief description of it, but I can’t find a pic anywhere.

ETA: It says “you can only see this in your eye” – Those slight eye movements are called saccadic eye movements. The strobe effect arises from the very brief persistence of vision in your retina as your eye moves slightly. So maybe that’s not something you could actually picture in a photograph.

When I first visited the Exploratorium about 25 years ago, I saw that vertical line of lights, but didn’t think much of it. Then several times when scanning the room, I would see an image of a cartoon eye, then look back to try to find it, but never could. It was several hours later when I got to the display that explained it that I realized what was going on.

About which cars do it - I was just going off my personal experience. I’ve noticed it at least several hundred times, and every single time, without exception, it’s been a Cadillac. YMMV.

Well, I’ve seen it many many times too. But, under the circumstances, those cars are always ahead of me, and it’s always at night. So I can’t say for certain if they’re all Cadillacs. But if so, that seems like an astonishingly large number of Cadillacs tootling around.

In 2009 it was mostly or almost invariably Cadillacs. I was able to impress my friends and woo women with my ability to identify a Cadillac at night from a mile away. I knew my ability wouldn’t last because it was only a matter of time before more cars would have stroby LEDs. I sent in a CarTalk Puzzler for this as a suggestion but, alas, it was never used.

Now adays its much harder to pick out the Cadillacs but I still can on occasion because their tail lights flash slower than others.

are known epileptics even allowed to drive?