Does turning on a car’s headlights increase fuel consumption?
0 voters
I’ve noticed that there are many in Forumosa that has had disagreements with the locals (colleagues, wives, girlfriends, traffic police) over whether turning on a car’s headlights will increase fuel consumption.
So what’s your opinion? Does turning on a car’s headlights really increase fuel consumption?
Does the pope shit in the woods?
Gasoline powered vehicles are only about 20% efficient, with so much of the power produced being dissipated as heat and internal friction. The charging system runs whether or not the lights are switched on, so I find it really hard to believe that the power consumed by the lights has any practical or even measurable effects on total efficiency. It’s probably several orders of magnitude less than the tiny amount of drag induced by underinflated tires.
As a useful guideline for saving fuel, the headlight/gas argument has no logical basis whatsoever… Remember, it’s often proposed by the same people who leave their cars idling with the a/c running while they pop into a store!
Technically yes, but the amount used is so low as to be essentially zero.
It’s not like the air conditioner in a car, which consumes a measurable amount of fuel (so I hear).
[quote=“Chris”]Technically yes, but the amount used is so low as to be essentially zero.
It’s not like the air conditioner in a car, which consumes a measurable amount of fuel (so I hear).[/quote]
So is that a “yes” or “no” vote? How low does it have to go before you’d consider it “essentially zero”? 1% of the total fuel consumption? 0.1%? 0.01%?
FYI, I’m not asking a loaded question here. I’m just trying to understand your answer because different people have different thresholds for “essentially zero”.
For example, if one gas station sells gasoline at (to use an US example here) $3.00/gallon and the one across the street sold it for $3.01/gallon, would you consider the price difference to be essentially zero?
What’s a gallon? We use metric…
The answer comes down to the 1st 2 basic laws of thermodynanics
Law 1 states you can’t win
Law 2 states you can’t break even
or put another way - there is no such thing as a free lunch.
So to use your lights without increasing fuel consumption would break these laws - as you would be getting the light for free.
The increased fuel consumption is also not as low as one might think.
From the Scotsman:
The AA Motoring Trust pointed to research from the Federal Highway Research Institute in Germany, which showed dipped headlights increased fuel consumption by 3 per cent, as extra power has to be generated.
http://thescotsman.scotsman.com/index.cfm?id=343052006
Appears to be a debate going on in Europe as there are moves to require all cars to come with the lights hard wired on.
What? No effect? Where does the energy come from then? Cosmic waves? The old Lonely Planet had this bizzare lights-don’t-use-fuel-let’s-all-have-some-free-energy notion, too, and I think it was supposed to be a jab at the locals for trying to save a dime.
Yeah, sure, the alternator is running all the time, but it’s basically free-wheeling until you put a load on it. Put an electrical load (i.e., lights) on the alternator and it will put a mechanical one on the engine. One guess where the engine gets all its power.
3% sounds a little high, but even 1% is significant. But AC is probably more than 10%.
I’m sure it increases fuel consumption, but it has saved my arse on my bike many times. Even idiots tend to notice the headlights of a bike!
So, increased fuel consumption vs. the cost of hospitalization because some dipshit didn’t see me? I’ll pay for the extra fuel any day.
So, yes, I disagree with the locals - I ride with my headlights on (bike not car); and, yes, I agree with the locals - it does increase fuel consumption … a tiny, little bit… not that I have noticed.
It must be true.
I get told this at least 3x’s a week by the locals.
Even the Fighting Ninja Amahs in my lane always point at my 'scooter headlight and waggle their fingers sideways.
But maybe that just another one of their secret fihting techniques…Ninja Amah Mind Control #31…
The lights are powered by the battery. The motor charges the battery, and in no way does it determine whether the battery actually needs charging.
As charging occurs whether or not the lights are on, turning the lights on does not increase fuel consumption.
Jeremy Clarkson asked Volvo to work out how much fuel was consumed by Volvos running with their sidelights on and they were unable to measure it it was so little.
Hilarious. Turning the lights on increasing fuel consumption. Whatever next? Of all the things in a motor vehicle that affect fuel consumption, the Taiwanese choose to put their lives and the lives of others in danger by running around with no lights on.
I have been told it’s nothing to do with worries about fuel consumption, but rather poor electrics running down the batteries leaving you unable to start your car. Or something.
Still giggling. Turning the lights off on your V6 Volvo estate to save petrol. Tee hee.
[quote=“Dr_Zoidberg”]The lights are powered by the battery. The motor charges the battery, and in no way does it determine whether the battery actually needs charging.
As charging occurs whether or not the lights are on, turning the lights on does not increase fuel consumption.[/quote]
It’s odd that by this logic the power of the headlights doesn’t seem to come into play. 1,000,000 candle power headlights that use no gas? Sign me up!
Charging does not occur when the battery’s fully charged and without load. Put a load on, however small, and the alternator’s electrical coils will put a load on the little turny thing inside, which will put a load on the belt, which will put a load on the engine, which will cause the US to invade Iran.
It may be a small amount of gas, but it’s still gas.
Another link:
iihs.org/research/qanda/drl.html#5
:bravo: But wait isn’t it law in Canada to have your headlights on all of the time? And you don’t see Canada invading anyone, right? Ha!
[quote=“Dr_Zoidberg”]The lights are powered by the battery. The motor charges the battery, and in no way does it determine whether the battery actually needs charging.
As charging occurs whether or not the lights are on, turning the lights on does not increase fuel consumption.[/quote]
So if I hook my car battery to the electrical grid, I can light all of Ontario and not use a bit of gasoline! Wow…I wonder why the government’s not doing it. It’s sure a lot cheaper than running all those nuclear plants. 
Here’s another article on the topic (with numbers and calculations): Driving with your Headlights On
It claims a 6% increase in fuel consumption during highway driving for medium sized cars and 12% for compact cars. The study by Germany’s Federal Highway Research Institute reports a 3% increase in fuel consumption but that includes all types of driving, not just highway cruising speeds.
Of course, the poll question was whether the headlights increase fuel consumption, not whether it wastes fuel. Because headlights during the day may serve a useful purpose, whether it is wasteful is up to the individual user.
Kudos to Skippy and myury for giving good explanations.
You know as well as I do one car battery does not generate enough power to supply a sufficient quantity of electricity to power Ontario. Furthermore, I did not say it doesn’t use gasoline, I said the same amount of gas is expended whether the light is on or not. Finally, in your scenario, fuel would be expended for the express purpose of recharging batteries that may or may not need charging. That is indeed wasted energy, and quite different from fuel expended by a motorvehicle, the express purpose of which is transportation.
While the link you provided was interesting, the author killed any credibility it had with this statement:
I’m amazed at how many people are wasting their time (me included) with this thread. Instead of concerning yourselves with whether or not my 125cc scooter uses an extra thimble of gasoline with the lights on, why don’t you concern yourselves with businesses all across Taiwan that crank the AC as high as it will go and then throw all their doors and windows open?
Mate, if you turn on your lights and then go to disconnect the battery you will find that the lights stay on. If you rev the engine. the lights will become brighter and when the engine comes back to idle, the lights will seem to flicker as the engine turns over - the battery provides a power balance when the engine can’t provide a constant flow to the electrical systems in use. While the engine does charge the battery, it also supplies power directly to the lights.
Another way to see this is by turning the engine on. As you are listening to the engine, turn on different systems like the lights, A/C and heated windows. The pitch of the engine will change as more loads are applied to it. This shows that the engine is working harder therefore using more fuel.
Because this is interesting, useless as it may seem 
I’m not an engineer, but I’m pretty sure this is false. It would be true for a a car with a generator because the amount of juice produced by a generator is directly proportional to RPMs. This is exactly why generators were long ago replaced by alternators. A properly functioning alternator should produce sufficient juice to power all systems in a car at idol RPMs. Only when the alternator has failed will the rest of the system start to draw off of the battery, which is exactly why many batteries have to be replaced at the same time as or shortly after the alternator has been changed out.
I was curious and did the same, save turning on the AC, on a 1979 MGB a few years ago, except I didn’t just measure engine load by ear. I did it with a manifold pressure gauge and a digital rev counter. There was absolutely no dip in RPMs and there was no change in manifold pressure (although if the latter changed, I’m not sure what that would have meant-we were just playing around with a friend’s guage). There was no change in the sound of the engine, either. The engine was at idol speed. I’ve never done the same “test” on another car, although my gut tells me that the sound of the engine did change a bit when electric stuff was turned on on an old Ford Bronco I used to have.
[quote=“sjcma”][quote=“Chris”]Technically yes, but the amount used is so low as to be essentially zero.
It’s not like the air conditioner in a car, which consumes a measurable amount of fuel (so I hear).[/quote]
FYI, I’m not asking a loaded question here. I’m just trying to understand your answer because different people have different thresholds for “essentially zero”.[/quote]
It’s a “no” vote for me.
No. I would buy the cheaper gas to encourage price competition.
Dangermouse wrote:
i think he’s right. but proof me wrong. always happy to learn
btw, have you ever noticed that many taxi-drivers turn the lights off at the red light? you think they do it to save fuel? a few years ago most taxis were as old as the drivers, there would be absolutely no point in that and frankly, they gave a damn about it. i asked a driver once, while he’s doing that and he said: ‘we always do it to save power from the battery (and carried on babbling something about a law…).’ - total misconception about how the engine and lights work… turns out its widespread
What about when taxi drivers put their cars in neutral at a stop? Does that save gas?
I read somewhere that in Japan, some drivers turn off their headlights at intersections out of kindness, to avoid blinding oncoming traffic. Dunno if it’s true and certainly wouldn’t happen in Taiwan for that reason 