Official Advice About When to Use Headlights is Nonsense!

In many states in the USA and in certain countries around the world, dreadfully unsafe guidelines still exist which say that headlights need not be switched on until half an hour after sunset and can be turned off again half an hour before sunrise.  This so-called advice is — and always has been — dangerous garbage.

Photo of two pedestrians dangerously standing half way across a road in very low light.
Two darkly-clothed pedestrians dangerously standing in the middle of the road (in the center, left-turn-only lane) in dawn light. Technically — because it was after dawn on this very gloomy winter morning and it wasn’t raining, vehicle drivers were not obliged by law to be using headlights, so imagine these cold, wind-blown pedestrians trying to get to work and not noticing an approaching vehicle with no lights. Not using headlights in low light is insanity but many drivers do it, and even more stupidly, the law allows it (in this case, in New York State)! Copyright image

It is also at least partially to blame for the fact that many drivers wrongly believe that as long as they can see where they are going, in low-light conditions, that is all that matters, but again this is dangerous.  A crucial part of the purpose of headlights is to more easily let other road users see you approaching.

Photograph of the speedometer and other dashboard dials, lit up at night.
If you are accidentally driving on your Daytime Running Lights [DRLs] your dashboard instrument lights will *probably* not be lit (to give you a clue) but check your own vehicle to find out if that is the case for you. Copyright image.
And it’s not just dawn and dusk that matter, either.  Some very important research, from various countries, has shown that driving with low beam headlights on at all times, reduces your chances of being in collision with a vehicle or person who — because they didn’t see you coming — drives or walks out in front of you, by between 14% and 28% (depending on the exact research criteria).  Does it need to be said that reducing the risk of T-boning another vehicle, or perhaps of you killing a pedestrian or bicyclist, by such a significant percentage is a really good thing?

Photograph of a pick-up trucke waiting to turn out of a side road, and in which the driver might be dazzled by sunshine when he looks to see if it is safe to proceed.
When the waiting driver checks to his left, towards our approaching vehicle, he may well be dazzled by the low sun, behind us, so this is just one example of times when headlights help your conspicuity greatly, even in bright sunshine. Copyright image.

So when should you use your headlights?

In terms of safety, Sweden was a long way ahead of the rest of the world on this subject — something which will not surprise true road safety experts around the world, because Sweden has long been one of the two best performing countries worldwide (along with Britain).

Back in 1977, it was made law in Sweden that all drivers must use headlights all the time, 24 hours a day, no matter what the weather… Period! Relevantly, this safety function is known as varselljus (“perception light” or “notice light”).  [My thanks to Barry Kenward for this useful insight.]

Photograph of a car in the foreground with no lights on, compared to vehicles in the distance which do have headlights on.
The vehicles in the distance are more conspicuous then the nearer vehicle because they have their headlights on but it doesn’t. Remember, conspicuity is at least as important even at a significant distance because it can persuade an oncoming driver not to commence a risky passing maneuver. Copyright image.

Eventually — meaning in the last 20-or-so years — some other countries belatedly started to realize the safety benefits of keeping headlights on, even on bright sunny days.  However, as it is a fact that vehicles do consume extra fuel — even though it is only a tiny fraction more — whenever additional electrical demands are placed on the vehicles, such as air conditioning or headlights, some conservation-minded people protested that using headlights at all times would increase the production of greenhouse gases and add to the pollution problem.

Photograph of a moving car's headlight beam at night, from the side.
The beam from Daytime Running Lights [DRLs] is typically not as powerful as that from your low beam headlights — one of the two safety reasons never to drive in poor light with only the DRLs. Copyright image.
As a result, Daytime Running Lights [DRL] were invented, and these used a bit less power on the headlights, to help reduce emissions.  So far, so good.  But some countries and automakers then very stupidly made a bad decision, which was that DRLs did not need to operate the rear lights as well, just the headlights on lower-than-usual power, because omitting the rear lights would save even more electrical power and the resultant but tiny amount of additional emissions.  The ongoing result of this is that drivers in such vehicles are commonly seen, driving around at night with no back lights at all and with DRL front lights which are not as bright as proper, low-beam headlights, so there is extra risk up front and significant danger from behind, especially in poor weather conditions.

I would stress at this point that I have always been a keen naturalist and now an enthusiastic conservationist, and I am by no means averse to cutting harmful emissions.  However, given the direct and undeniable risk to people which occurs when vehicles are driven without adequate lights and are therefore not seen until too late, which issue has to take priority?

Tongue-in-cheek, you should note that no automakers have decided to devote less power to their in-vehicle air conditioning — something that certainly would save more power and therefore more emissions.  In other words, the hypocrisy from automakers is that they will reduce the safety of road users but they will not consider reducing the comfort of their customers, even though environmentally it would do more good.  Putting comfort (and, of course, profits) before safety!

Photo of a road sign requiring "headlights on at all times for safety.
Even though signs like this are typically only used on certain roads and in only a few of the states, this sign actually says it all: Headlights on at ALL times for safety! Copyright image.

So what IS the best advice, in terms of greatest safety?

Here’s a list:

  1. Do NOT rely on Daytime Running Lights [DRL].  We are all human and if something else is on your mind it is all too easy to forget that in low light or poor weather you have no back lights to protect the rear of your vehicle.  Many people undoubtedly have been killed or seriously hurt as a result;
  2. Do NOT rely on automatic headlamps that switch themselves on when a light sensor tells them to.  As with many automatic things, circumstances can sometimes create the wrong outcome and you wont have lights when they really are needed;
  3. IGNORE any rules or guidelines that mention sunrise and sunset.  Even the bright, low sunshine and contrasty shadows that occur before some sunsets and after some sunrises can create situations where vehicles are hard to see;
  4. The common rule about “Wipers On, Lights On” is also INADEQUATE — written, as is so often the case, by somebody with inadequate knowledge who merely thought it was a good idea.  The fact is that many weather conditions such as heavy cloud, mist or lightly falling snow can easily take the light down below the sensible threshold at which lights definitely should be used, even if wipers are not needed! (See the photographs.)
  5. NEVER drive with just the front sidelights (a.k.a. position or parking lights) illuminated, even where there is good street-  or road-lighting.  Sidelights are not adequate for your conspicuity.
  6. What do we do at Advanced Drivers of North America?  That’s easy to answer.  We use at least low-beam headlights, and therefore rear lights too, 24/7.  Does that increase our vehicle emissions?  Yes, undeniably, but by a miniscule amount.  And is the safeguarding of human lives more important?  We think the last question answers itself.

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