q Lighting the Way with Daniel Stern (Part 2)

Lighting the Way with Daniel Stern (Part 2)

Last week we ran Part 1 of my interview with Daniel Stern, a vehicle lighting expert. This week, Daniel discusses when not to use your front fog lamps, what rear fog lamps are, whether you need to dip your high beams at night, and what can be done about those “phantom vehicles” traveling at night with only […]

Lighting the Way with Daniel Stern (Part 2)

Last week we ran Part 1 of my interview with Daniel Stern, a vehicle lighting expert. This week, Daniel discusses when not to use your front fog lamps, what rear fog lamps are, whether you need to dip your high beams at night, and what can be done about those “phantom vehicles” traveling at night with only their daytime running lights on.

Daniel is based in Vancouver, BC, and Seattle, and serves as Chief Editor of the industry’s technical journal, DrivingVisionNews.


ML: A big pet peeve I have is that drivers often have their fog lights on indiscriminately at night, which unnecessarily blinds people. Can you talk about that?

DS: You’re right again. Studies have confirmed that people use their front fog lamps at night regardless of weather. Front fog lamps are usually mounted low on the front of the vehicle, but they tend to be very glaring for a couple of reasons: While they use many of the same types of bulb or light sources as headlamps, they tend to be much smaller, and—here again—a smaller lamp of a given intensity looks brighter and more glaring than a larger one. And we pay even less attention to front fog lamp aim than headlamp aim; many front fog lamps aren’t even properly aimable because there’s no law requiring them to be.

The fact is that front fog lamps are of almost no real use to most drivers in most conditions. Many drivers are not well informed about what front fog lamps will, won’t, can, and can’t do, and they just run them all the time, assuming that more light’s better than less, right? Well…no. It depends on where that light falls, and front fog lamp light is essentially useless.

The human visual system is a lousy judge of how well it’s doing. “I know what I can see!” feels reasonable to say, but our subjective impressions tend to be very far out of line with objective, real measurements of how well we can—or can’t—see. The primary factor that drives subjective opinions of car light performance is foreground light—that is, light on the road surface close to the vehicle. Front fog lamps produce nothing but foreground light, which is almost irrelevant to safety; it barely even makes it onto the bottom of the list of factors that determine the safety performance of a car lighting system.

A moderate amount of foreground light is necessary so we can use our peripheral vision to keep track of the lane lines and keep our focus higher up the road where it should be, but too much foreground light works against us. It tends to draw our gaze downward, and the bright pool of light causes our pupils to constrict, which destroys our distance vision. Yet it creates the illusion that we’ve got good lights because our visual system just doesn’t work the way it feels like.

Besides, front fog lamps produce beams with very short reach. At speeds above 25 mph, you’re going to hit whatever the front fog lamps illuminate in front of you. So that really kicks the legs out from under arguments about using the front fog lamps to reveal deer and other critters just off the roadway. The best three things you can do with your front fogs: Turn ‘em off, leave ‘em off, and forget they exist.

ML: What about rear fog lights?

DS: I’ve been saying “front fog lamps” here because that’s not the only kind. There’s also the rear fog lamp, which is totally different. It’s an extra-bright red tail light that drivers can switch on in heavy fog, snow, or rain to make themselves more visible to following drivers when bad weather makes it hard to see the dimmer regular tail lights. Rear fog lamps are required in Europe. They’re not required here, but they’re allowed.

YouTube video courtesy of Toyota Malaysia.

Many European cars and a sprinkling of others come equipped with them in North America, but most of us in the States are unfamiliar with rear fog lamps. Too often, the switch gets turned on—and left on. In clear weather, these bright red rear lights are intensely glaring for following drivers, who also may have a harder time detecting the similar-looking brake lights next to them.

The icon for the rear fog looks like the symbol shown below, so if you have a Volvo, Audi, BMW, Mercedes, or another European car, find that switch and turn it off. Turn it on only when the weather is soupy enough that you wish the car in front of you had a brighter tail light, and turn it off again once the weather clears.

Lighting the Way with Daniel Stern (Part 2)

ML: Just how well do automatic dimmers work in modern cars (that switch from high beams to lower ones automatically)? About 8 years ago, I rented a Lincoln and they did not work very well.

DS: For many years, automatic beam selectors were based on simple light detectors and worked poorly. Today, they tend to do a much better job; they’re camera-driven and have much more intelligent control algorithms.

ML: Just how necessary is it to dip your high beams at night when you’re traveling on a large divided highway with a very wide median?

DS: This is an interesting question and the answer’s neither simple nor intuitive.

US regulations require fairly wide light coverage from the high beams, but this can be achieved in different ways. Some cars shift the entire beam downward-rightward for low beam and upward-leftward for high beam. With these, you must be very widely separated from oncoming traffic before you can safely use your high beams.

Other cars keep the low beams lit and just add another pair of lights when high beams are activated. Often these dedicated high beams provide a tight spotlight that reaches down the road with extra distance while relying on the still-lit low beams to provide the width. This system doesn’t require such wide separation to avoid dazzling oncoming drivers, so if your side of the road is empty and a reasonably wide berm lies between you and the other side of the highway, you can carefully use your high beams.

By the way, not getting flashed isn’t a dependable indication that everything’s okay, because most drivers won’t flash a glaring car, so you must pay attention. If you’re lighting up the backs of road signs in the other direction, you’re also blinding oncoming drivers. And the angles involved on curved roads can mean your high beams are shining directly into other drivers’ eyes.

Lighting the Way with Daniel Stern (Part 2)

ML: Last but not least, there is the phenomenon of “phantom cars.” Many drivers don’t realize that their headlights, sidemarkers, and rear tail lights are not on at night because their daytime running lights (DRLs), which are very valuable for daytime safety, are getting brighter and they mistake them for headlights. The whole problem could be solved if manufacturers simply make the instrument cluster lights come on only when the headlights are switched on. What are your thoughts on this?

DS: This is a real and serious safety problem, and you’re absolutely right about how the dashboard lights ought to work. In the past, all vehicle visibility systems were controlled by the driver, who switched the headlamps on and off (and the instrument panel, license plate, parking, tail, and sidemarker lights along with them), selected high or low beam, and activated the windshield wipers and washers as necessary. Those tasks have been automated over the years to varying degrees—and that variance is now causing problems. Some (but not all) cars automatically switch on the headlamps or change from DRLs to full nighttime lamps with the rear and side lights when it gets dark.

The original idea was to have the lack of dashboard illumination nudge the driver to turn on the lights, but that never worked reliably in brightly lit city streets, so some drivers blundered along in dark cars. Drivers without automatic lights would sooner or later find themselves in the dark, with no instrument lights or pool of light on the road ahead. Sometimes opposing or following drivers would blink their headlights to alert oblivious drivers. All of that was at least sometimes enough to jog drivers’ attention and they’d switch on their lights. If not, they were probably drunk or otherwise impaired, and sooner or later a police car would flash the other kind of lights and get the sloppy driver off the road.

YouTube video courtesy of DJLToronto_DashCam.

But today’s mix of automation and infotainment has thrown sand into those gears. For one thing, there’s no such thing as a dark dashboard anymore. Most cars have instrument panels, consoles, touchscreens, and a panorama of controls and displays illuminated whenever the car’s running, night or day. So, subtract that from the toolbox of indicators. (And let’s be realistic: Drivers often don’t know, care, or think about what a little green or blue pictogram of a light on their dashboard might mean.)

Remember that in a car with DRLs, the driver sees his lights reflected in the vehicle in front of him, or on the wall or window in front of his parking space. So, remove that from the toolbox, too. DRLs are both inadequate for nighttime driving vision and they produce more glare than low beams—two more safety hazards. And most drivers can’t reasonably be expected to think, “Hey, this oncoming car has only its DRLs lit, not its nighttime headlamps; I’ll blink my lights at them to let them know!” So now the toolbox is empty.

DRL regulations in North America tend to be driven primarily by Canada, where DRLs are mandatory—in the States, they’re allowed but not required. Transport Canada (the Canadian equivalent of NHTSA) has recently acted to require automakers to choose from three solutions to the problem:

  • Fully automatic light management, whereby the vehicle switches from DRLs to full nighttime lights at a certain ambient light threshold.
  • Light the tail lights with the DRLs.
  • Don’t illuminate the dashboard unless the headlights are on.

Are these reasonably adequate fixes? The first one is, but the other two are not. Here’s why: The always-lit dashboard is not likely to go away any time soon because today’s instrument panels are far too integral to the vehicle’s general controls (HVAC, sound system, navigation, etc.) to make them invisible until the driver switches on the lights.

Besides, this would aggravate a problem that’s existed for decades: Faced with a dark dashboard, thoughtless drivers slap at the headlight switch until the dashboard lights up. That turns on the parking lights, tail lights, and the sidemarkers but not the headlamps. Unfortunately, North American regulations require that the dashboard must illuminate when parking and tail lights are lit, and the DRLs must not extinguish unless the headlamps are switched on.

So, the driver gropes at the headlight switch to light the dashboard, DRLs, and parking, tail, and sidemarker lights. It’s better than total darkness at the sides and rear but still inadequate for the driver and pedestrians. It’s also dangerously glaring for other drivers.

Having the tail lights lit with the DRLs amounts to the same thing but without the driver’s hand sweeping at the headlight switch—a perfect recipe for many more cars driving around at night with tail lights (good) and DRLs (bad), and an even stronger false signal that the car has automatic lights.

Car Headlight Instrument Switches

One might object here to figuratively wiping the driver’s nose and argue that anyone adult enough to earn a driving license should be expected to operate a car correctly. That’s fair, but proper user interface design requires that correct operation be as intuitive as possible—and that the path of least resistance should make it easier to get it right than wrong.

So, the best way to solve the problem without creating new ones is to remove the driver completely from the task: The car activates daytime lights in the daytime, nighttime lights after dark. The technology to do this is simple, cheap, and reliable. And we’ve had it for many years. Mandatory automatic lights are the only reasonable, rational, realistic solution. All that stands in the way is automakers’ desire to monetize every last little bit of the car that isn’t strictly required by law.

For that matter, one of the world’s top vehicle lighting research bodies, the Rensselaer Polytechnic Institute’s Lighting Research Center, has shown a clear benefit (fewer crashes) of “headlamps on when wipers are on” laws. With the reduced visibility and increased light scatter caused by rain and snow, low beams are the appropriate front lights, DRLs are inappropriate, and side and rear lighting are crucial. [Mi Ae’s note: I recommend driving with all your lights on during the day if the weather is cloudy, foggy, rainy, or snowy, or at any time when visibility and lighting contrast pose critical safety issues—e.g., brightly dappled forest, potential overtaking on a two-lane rural road, or high-glare situations. Even during the days you can never be seen too much!]

Why then do automakers not add a single line of software code (at most) to their car control modules to activate the full lights on low beam if the windshield wipers are activated for more than a short duration? This, like automatic day and night lighting, is inexpensive, low-hanging fruit to fuel the drive toward zero traffic fatalities.

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Mi Ae Lipe

Mi Ae Lipe is a citizen advocate living near Seattle, Washington. She blogs on Driving in the Real World, Tweets daily driving news and tips at @DrivingReal, and writes a regular column on street driving for BMW CCA’s Roundel magazine. She frequently collaborates with government organizations, NGOs, and individuals. She and fellow citizen Mark Butcher are recipients of the National Highway Traffic Safety Administration (NHTSA) 2017 Award for Public Service for their work in


  1. I have long thought that many owners/drivers treat their fog lights as automotive jewelry, on the same plane as allow wheels. [Why do automotive enthusiasts resist steel wheels painted black? = “NASCAR style?” In sequential steps since 1980 I have replaced incandescent headlights with halogen, and sealed beam halogens with european optics, and incandescent brake lights with LED bulbs, for faster light-up.
    Progress? BP

    • Careful on that last step you mentioned. The overwhelming majority of “LED bulbs” marketed to replace incandescent brake and signal lights are unsafe, illegitimate junk, and the ways they’re unsafe are not necessarily obvious or intuitive. Perhaps that should be part of a future column here!

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Lighting the Way with Daniel Stern (Part 2)

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