What is the MPG penalty of headlights on?

I doubt that anyone knows, but I am sure you will still get some answers.

 

There was an older thread on this; I'll suggest my post since it's obviously the best one in the thread, IMNSHO. But there's some interesting additions to my rough estimates in the thread too.

Bottom line; it's less than 1 mpg. If you're worried about safety, turn them on. A gallon of gas has enough energy to run your headlights for several days continuously.

 

Very little impact, but it is why daytime automatic lights aren't offered in the U.S. If it's dark or raining, I recommend using the headlights!

 

I don't notice much difference with the headlights on but I do find the HV battery runs down noticeably quicker if I have my front fogs on with the headlights.

Coincidence?

 

The difference will be small enough that you won't be able to get a close to accurate number by comparing overall mpg.

If you add up the wattages of the lights that are on with the headlights and make some reasonable assumptions about generator and ICE efficiencies, you will be able to calculate the fuel consumed to illuminate the lights.

 

I turned my lights on the minute I picked my car up the day before Thanksgiving 2004 and haven't turned them off since. The reason I did this is because I had a small red car in the land of SUVs and trucks at the time. My last tank I got 50.3 MPG and I live exactly 2 miles from work.

Oh and BTW I haven't replaced a headlight yet. I replaced an indicator light on the driver's side this past July.

 

even tho it may be 1 mpg or less, imagine how that adds up across the country and world!

 

If I remember right, Halogen are about 150 watts/pair, and HID half that amount.

The least power demand not including lights might be around 5 kw, and a maximum maybe around 20 kw. Think driving 35 mph on a country road with no stops, vs screaming down the highway at 80 mph.

So, the additional energy use is 5.15/5 for the easy life, and 20.15/20 for the lead foot.

As you can see, the lead foot wins ;-)

 

Give me a distance, elevation change, and round trip average mpg, and I'll give you an estimate of the difference likely attributable to the elevation. This will be based on a rule of thumb of an extra gallon of fuel per 10,000 feet of elevation gain, give or take 10-15%.

 

This question is impossible to answer without knowing the speed of the vehicle. Headlights are a fixed load, consuming the same amount of fuel at speed or standing still. At low speeds, the mileage hit from headlights is considerable. At high speeds it is negligible.

Regardless of speed, 150W headlights are equivalent to 0.2 hp, or 1/5th of a hp. That isn't very much compared to what it takes to move a car.

Tom

 

Here's a fun one for you Tom,

How much weight would one have to lose in order to make up the 0.2 hp loss due to having the lights on?

 

have you figured in the pressure from the photons pushing against you >

 

Good point. We need to factor that in, including the positive thrust from the tail lights.

Tom

 

Yeah, the Standard Halogens are 55w each on Low. The Taillights and others that come on probably bump it to ~150w. The normal electronics in the car use significantly more than this when the car is Ready.

I doubt it's effect could be measured in real world mileage tests. (the noise in those measurements is higher)

 

I thought about that, but it would be offset by brake drag. How much depends on how hard you press. I suppose if you just gently ride the brake pedal you could get some photon assist. We need to do more testing.

Tom

 

decrease in 0.54389487329572542 mpg

 

It's an easier consideration for EV's. You lose approximately half a mile of range for every hour your headlights are on.


Plus I didn't think you'd get any thrust from photons, because they're massless?