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Do Car Headlight Use Gas? (What About Daytime Lights?)

Do Car Headlight Use Gas? (What About Daytime Lights?)
Fact Checked and Reviewed by: Kris Jackson, ASE-Certified Mechanic
Kris Jackson has been a mechanic since 2010 after graduating from UTI. He’s worked with several master mechanics and holds several ASE Certifications. You can read more about Kris here.

There are a lot of ways to save on gas and improve your vehicle’s fuel efficiency. But one of the not-so-good options would be driving without headlights and it doesn’t matter how much you’ll save- going dark isn’t worth it!

Still, figuring out how much fuel headlights use is interesting and even more so when you consider optional daylights. So how much fuel do all the various headlights use? 

Because headlights are powered by a car’s alternator, which gets power from your gas-burning engine, there is a slight increase in fuel consumption when they’re turned on. However, the difference is almost impossible to notice. Standard halogen bulbs, used in 80% of cars, add minimal costs. If gas costs $3.00 per gallon we estimate that high beams cost $0.04/hour, low beams $0.035/hour, and daytime running lights only $0.0129/hour.

That’s the quick answer and is enough to keep your wallet happy and your headlights onBut we’re going to take a much closer look at everything you need to know about high beams, low beams, running lights and fuel efficiency. So stick around if you want to learn more. 

Let’s get started! 

What Powers Your Headlights? 

Headlights are powered by electricity generated by the car’s alternator while the engine is running (and your battery if the engine is off). That’s true of most accessories in your car from the radio to the A/C. The alternator is powered by the engine, which is powered by gas and so headlights do consume fuel, even if it’s somewhat indirect. 

When the car’s engine is running, the alternator produces electricity and when you flip the switch to turn on your headlights, the alternator works a little harder to power them up. For daytime running lights (DRL), it all starts as soon as the car’s engine is turned on.  

The alternator is powered by the engine, which of course uses fuel, so more work from the alternator means more work from the engine. That’s the simple and high-level overview of your headlights (with a focus on fuel usage) but if you’d like a much deeper look at how your car’s headlights work check out this video: 

How Much Fuel Do Headlights Use? 

Okay, we understand that headlights do use fuel but just how much? We’re going to assume standard halogen bulbs for this section since that’s what’s being used by 80% of the cars on the road today. We’ll look at a few other bulb types, and how they impact fuel costs, later in the article. If you’d rather just get to the point, you can check out this table for the quick answer: 

Fuel Consumption for Halogen Bulbs
Headlight Type Wattage (for 2 bulbs) Fuel Consumption Increase (gallons/hour) Hourly Fuel Cost at $3.00/gallon
High Beams 130 watts 0.014 $0.04
Low Beams 110 watts 0.011 $0.035
Daytime Running Lights (DRL) 40 watts 0.004 $0.0129

High Beams

Typical halogen bulbs are rated at around 65 watts each. So for two headlights, you’re looking at a total of approximately 130 watts.

Now it’s time for a little math. 

We know that 1 horsepower equals 746 watts which means the horsepower demand is roughly 0.174 horsepower. Now let’s imagine our engine is putting out 200 horsepower and consuming 16 gallons of fuel per hour. A demand of 0.1743 horsepower from the headlights on high beam means we end up with a 0.08715% increase in power use and increases fuel consumption by a very small amount of 0.014 gallons per hour (0.0008715 x 16 gallons).

Assuming a fuel price of $3.00 per gallon, operating the high beams leads to an estimated increased fuel expense of about $0.04 per hour.

Low Beams

Typical halogen low beam bulbs for cars are rated at around 55 watts each.

For a pair of headlights operating on the low beam setting, the total wattage comes to approximately 110 watts. Converting this to horsepower, given that 1 horsepower is equivalent to 746 watts, our headlights demand about 0.147 horsepower.

If we consider an engine producing 200 horsepower and consuming 16 gallons of fuel per hour, this 0.147 horsepower demand from the low beam headlights results in a 0.0735% increase in power usage. This translates to a slight rise in fuel consumption, around 0.011 gallons per hour.

With a fuel price set at $3.00 per gallon, the cost of running low beams adds an estimated $0.035 to your hourly fuel expenses. 

Daytime Running Lights (DRL) 

Daytime Running Lights (DRLs) are typically lower in wattage than high beams but typically use the same halogen bulbs, with many halogen-based DRLs consuming only around 20 watts each.

That means two DRLs, one on each side, is about 40 watts. As we’ve already done for the other types of headlight functions, let’s translate this to horsepower where we get 0.0536 horsepower. Now, when we think of an engine churning out 200 horsepower and burning 16 gallons of fuel per hour, the additional power needed for the DRLs results in a 0.0268% rise in power utilization.

That’s not much but if we keep this going we can estimate that it will increase fuel consumption but around 0.004 per hour. 

With a fuel price of $3.00 per gallon, two DRLs contribute to an almost negligible increase in your hourly fuel costs by about $0.0129.

Should I Turn Off My Daytime Running Lights To Save On Gas? 

The average person drives around 293 a year. If you drop your DRLs for a full year then you might save around $3.77. 

For most folks, that’s not enough to worry about. But if you’re considering earning yourself half a Starbucks coffee at the end of the year by dropping your daytime running lights, consider that one study found fleet vehicles with daytime running lights had 7% fewer accidents during daytime hours. I’d happily pay $3.77 a year to reduce the risk of an accident by even a fraction of a percent let alone anything close to 7%! 

In many parts of the world, there are specific laws and regulations around the use of DRLs that require them to be on at all times. For example, in Canada, all vehicles manufactured after December 1989 must be equipped with DRLs. Turning them off, modifying them, or disabling them could be a violation of the law. In the European Union, similar rules apply to cars and small vans registered from February 2011 onwards.

When it comes to other headlights, leaving them off to save on a gas isn’t even a question! 

Does The Type Of Bulb Matter?

Yes, the type of bulb can make an impact on how much fuel is used but since we’re already talking about very small numbers (at least in terms of currency) the changes between bulbs make very little difference. 

Still, let’s quickly look at two of the big alternatives to the standard halogen bulb: 

LED Bulbs

LEDs are much more efficient than halogens and this can make a huge impact in other areas of life but aren’t such a big deal when it comes to your mpg. A typical LED headlight might only use 20W to 30W compared to the 55W to 65W of a halogen. Even half the wattage will still barely safe a penny based on our estimated fuel costs though. 

HID (High-Intensity Discharge) Bulbs

These can vary but typically consume around 35W and 70W combined. That’s actually more than halogen, albeit not by much.

Laser Bulb

There is a newer type of bulb that hasn’t all markets yet but it’s the even more energy-efficient laser bulb.  

What Happens When The Car Engine Is Off? 

When you turn on your headlights without the engine, your headlights are being powered completely by the battery. However, once the engine is turned on, the alternator will have to work harder to recharge the battery. 

It’s not a lot, but that extra work will burn more fuel as the engine provides the power needed by the alternator to recharge the battery. 

Still, this is all pretty insignificant when you look at the actual fuel consumption or the pennies per hour that it will cost to run. This is the same thing that happens to many other electronic accessories in your car from the heater to the fuel efficient radio and everything in between. 

Closing Thoughts

When it comes to headlights, their impact on fuel consumption is, in the grand scheme of things, minuscule. If you picked up every quarter you found on the ground in a year, you’d be pretty close making the same amount you’d get from skipping DRLs,

And while the type of bulb does influence power consumption, the difference in fuel costs between bulb types is, again, nearly imperceptible.

But while comforts like heated seats (which don’t use much fuel eithercould be skipped to save a few pennies headlights are different. Even daytime running lights serve a critical safety function and they’re closer to vehicle essentials like your defroster

In some places, there isn’t even a choice, and regulations in many parts of the world mandate the use of DRLs, emphasizing their importance in vehicular safety. So while it’s intriguing to delve into the nitty-gritty of how headlights impact fuel consumption, the broader takeaway is clear: the safety benefits of using headlights, particularly daytime running lights, far surpass any minuscule cost savings one might achieve by turning them off.

When it comes to driving, safety should always be the priority. So, keep those lights on, drive responsibly, and let the pennies take care of themselves. Ride safe!

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