Why Car Lights in US are Always On

Just one quick question: why people in California always have their car light on even in day time? It seems waste of energy, and pretty annoying. On the rented car, the light switch default to AUTO, but does it mean to shut it down in automatically in sunny California at day time?

BTW, I inherited this habit of forgetting to close the light when I am back to Shanghai (completely manual lights), and Wendy always reminded me about that.

25 thoughts on “Why Car Lights in US are Always On

  1. In Denmark, having lights on all day is required by law. I much prefer it that way and always had my lights on when driving in China. Of course the lights are useless for illumination, but they are very useful for identifying moving cars at a distance because it is easier to notice moving light sources than to identify the shape of a car and looking at their much weaker signal


  2. The headlights are definitely for other cars to see you better, than to help you see better. As you noted, it is useless for the latter purpose in broad daylight. In the US, it is required by law to have headlights on when it’s raining, with the rule of thumb being that headlights should be on if your windshield wipers are on.

    Most newer cars now have the AUTO headlight feature. It turns on the lights automatically when you turn on the engine, and it also shuts the lights off automatically when you turn off the engine. Some cars even have smaller daylight driving lights designed specifically for this purpose.

  3. In many states in the US it is the law to have lights on during the day. It does not waste any energy as the engine is running, the alternator is recharging the battery. It would waste battery if you left them on after you turned off the engine, but most American cars automatically shut them off when the engine is off anymore.

    It does help with visibility of on-coming cars, like a gray car on a gray day.

  4. does your car in Shanghai beeping if you pull out the car key without turning off the headlights?

  5. I am not aware of this law “In many states in the US it is the law to have lights on during the day.” although I have driven in many states in last 10+ years in the US.

    The only reason I can think of is “we are Americans, we don’t care” or “even if we use world 25% of oil with less than 5% of world population, so what”.

  6. @GN, my car actually turns off the light when the engine goes off, so I typically don’t bother to turn it off. But the second morning, when I start the engine, it is on, and I need to mannually turn it off.

    In Shanghai, I would say, NO car turn the head lights on in the day time – well, there may be one or two of this car I see once in a month, but it is really rare.

    I don’t know if there is any law to require it to be off, but I remember I saw a TV drama which the driver was stopped by policeman just because he had his car light on in day time.

  7. In Canada, lights on while driving is required. In fact, a lot of cars when put into gear will turn on the light, no matter your light switch is on or off. I think it has to do with the northern weather. It’s generally more gloomy in the north, especially in the winter snowy days, which are exceptionally long.

  8. This is Day Time Running Light and is the standard equipment in all vehicle sold in U.S. and Canada. The devise is operated on 25% of the high beam capacity as to enhance the visibility of the appraoching vehicle during day time but does not cause glare to the driver.

    During night time the driver still needs to turn on the standard lighting as DRL does not activate the tail lights and low beam.

  9. I lived in CA and OR… neither has a daytime-headlights-on law. And I have a 4Runner and an old Mersedz, neither turns headlights on automatically. On the roads, there are always signs at areas where lights on are required, tunnels, mountain area, and forests roads… etc. And you do know that you need to turn on the lights when it’s raining or foggy… that’s commend sense. We had one night driving out for Chinese food takeout forgot to turn on the headlights got pull over and was told to turn the lights on… that’s it.

    It is a safety issue… it doesn’t use any more energy, and it maybe a nice option to have for some people… elderly, for example.


    @STLPlace, Take A Hike… 八杆子打不着的。

  10. In Switzerland as is the case in northern Europe, this is required at all times. It seems useless, I know, until you look in the back mirror — trust me, a car with its lights on is instantly more recognizable than one without it.

  11. This is another one of those issues that people never stop arguing about. “It does have an effect”, “It does not have any effect”, “It disturbes oncoming traffic”, etc. etc. Consult the Wikipedia entry for a more rather take on this issue: http://en.wikipedia.org/wiki/Daytime_running_lamp

    By the way, for those claiming that DRL does not consume any extra energy: I think it is time you pull out your old middle school physics text book.

  12. OK… don’t think I know my physics… is there any actual date on this? I searched online, it is another he says she says issue… sounds like it should be submitted to Mythbusters.

  13. Stephen is right, these are running lights which are different from the headlights you turn on at night. What you are seeing is not people “turning on” their headlights during the day (I don’t think anyone in the US does this) but new cars that have running lights on automatically. I believe it’s now a requirement for new cars.

    Bonjour Thomas, please don’t be so literal. Of course lights require energy. The point is that the car is generating electricity anyway when the engine is running, so the running lights are not decreasing your gas mileage – at least, not to any measurable extent. So STLPlace, your comment about how much oil Americans use is pointless here, but thanks for trying, we love you too.

  14. Stephen is right, what you are seeing is running lights, which are different from the headlights that you turn on at night. I don’t think anyone in the US purposefully turns on their lights during the day under normal conditions, but a lot of new cars include this equipment automatically. I actually thought it was a requirement for new cars, but according to the Wikipedia article not so.

  15. It is rediculous to think that daytime running lights do not use energy “to any measurable extent”. When you are talking about tens of millions or hundreds of millions of cars with daytime running lights the additional energy usage is measurable, large and completely unnecessary. It would be one thing if these lights had built in sensors to only turn on below a certain level of ambient light, but daytime running lights that are always on are horribly ineffecient, wasteful, and have not been proven to increase safety.

    I’m glad Wang Jian Shuo mentiond this – it’s easy for someone who hasn’t seen this type of running lights before to recognize them and question why they are being used if they are wasting energy and not necessary.

  16. The DRL is designed to increased the conspicuity of the vehicle and to avoid possible accident, since accident never happens, how can statistics show the positive comparison especially when DRL have been installed for almost 20 years.

    Nevertheless, I hope you don’t treat DRL like the “light pollution”.

  17. Please disable DRL as it wastes energy and has no effect or increase accidents rate. Plus, people forget to turn real headlights on when raining. I had to cut a wire on my car computer to disable it with guidance from the car manufacturer bulletin. Pulling the fuse didn’t work.

  18. As to whether or not DRL reduces accidents, I receive a discount on my car insurance because my car is equipped with them. I’m not inclined to believe my insurance carrier would offer that incentive if it did not benefit them in the form of lower risk of accident.

  19. Actually, daytime running light will never use much energy because most of the time the car battery is full or 80% full. As a result, under most cases, the electricity generated by the electric generator is wasted after the car battery is fully charged. So, listen to music and small light should not affect the energy usage unless you are driving a electric car. If you don’t believe me ask somebody who is an M.E. or something.


  20. I always turn on my lights manually (in the USA). My car is small, and grey. So it is the same color as the road, and hard to see, and people pull out in front of me. With the lights on it’s better. So this is one person who does it. You’d think that other people would be able to see a car. But sometimes not!

    It’s true that it does take a bit of energy to spin the alternator to generate the electricity for the lights. The lights are HID so they don’t consume as much power as regular lights. But even so, the 55W of regular headlights is very small compared to the energy of accelerating 1500 kg of metal which ultimately is dissipated as heat in the brakes, or wind drag.

    I agree with one of the posters who pointed out that people with DRLs sometimes forget to turn on the real lights when needed. The biggest problem then is that the tail lights are not on, so you could be hit from behind.

  21. I think the statement about the car battery is most time full or close to full is not correct. If you drive freeways and long trips, yes, it may be very close to full. But if you trips are local and short, the energy used to start the car and power the rest of the electronics and is equal or more than the battery gets charged.

    I agree that for a small, gray car, maybe the lights would help. But if one can’t see a big vehicle moving on a road, then that person really should not drive.

  22. Driving with lights on benefits road safety, as it will improve the visibility and it will be easier to identify a moving car with lights on.

    I’m from the United Kingdom and I always put the lights on no matter what the weather is.

    Sadly, most people in the UK don’t put their lights on. Which is stupid, in my opinion.

    However, new cars from 2010 and some from 2009 are equipped with DRL (Daylight Running Lights) which is great!

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  24. These DRL’s make sense in far northern climes where daylight is greatly reduced during winter. Some areas have no sunlight at all for months. These do not make sense in areas further south where daylight is much more plentiful during the winter.

    Being conspicuous should not be an issue. Humans are preditors. Our eye face forward. We are wired to detect movement be it errant vehicles or that ball bouncing in front of our car which a child is about to chase into the street.

    I am far more concerned with bycycles with minimal lights and pedestrians who wear dark clothing while walking on roads.

    I would be interested in finding statistics on crashes from major insurance companies. If these use of DRL over that past 20 years indicate reduction in crashes, reducing our premiums, then I’ll be convinces DRL’s make sense.

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