Lights on = lower mpg?

[DBaum]

I noticed when driving with my lights on ( because I have to since I work nights so it's always dark to and from work ) that my mpg is pretty bad. My girl friend always drives when there is light out in her prius so she seems to get about 2 mpg better then me all the time. Is there any way of improving this? I have a III so no LED lights. That would of came in handy for me. Anyone know of light bulbs that use less electric but still bright as the OEM?

[ScottG10]

I'm very new to the whole Prius scene and we only have about 500 miles on ours but during a 2 hour freeway trip in the dark and rain we got 50 mpg. That seems good to me for driving 65 MPH with three adults and the heat set at 75 in the car but I'm curious as to how much better it would have been on a nice mild day.

[PriusCrazy]

Originally Posted by DBaum

I noticed when driving with my lights on ( because I have to since I work nights so it's always dark to and from work ) that my mpg is pretty bad. My girl friend always drives when there is light out in her prius so she seems to get about 2 mpg better then me all the time. Is there any way of improving this? I have a III so no LED lights. That would of came in handy for me. Anyone know of light bulbs that use less electric but still bright as the OEM?

Hi DBaum,

I'm sure the experts will chime in, but I believe things like the lights are powered by the 12V battery, not the "big battery". Running the heater will definitely affect mpg though...

I've noticed on my IV with heated leather seats, I can turn the heated seats on and the engine will not run, but the second I hit the heater switch (with or without heated seats on) the engine will fire up.

Maybe you should take note of your girlfriends driving techniques and try some of them?

[DBaum]

Maybe you should take note of your girlfriends driving techniques and try some of them?

Her commute to work is 95% highway. Mine is 25% highway. I'm sure that is also another factor...

[GrumpyCabbie]

I have found that if I use the front fog lights the big battery appears to discharge much quicker than if I just use normal lights causing lower fuel economy. Can't imagine that two extra bulbs makes much difference but my experience suggests it does. I also find that very wet roads after/during heavy rain can also severely affect fuel economy.

Anyone else found this?

[stream]

It's been raining like crazy for the last week here (standing water in streets very common). Before this week I was averaging ~48 MPG. This week, I'm averaging 44.5, or a 7% decrease.

I attribute it to increased rolling resistance due to water on streets, and increased battery use due to headlights and wipers.

[mayfirst]

Originally Posted by DBaum

I noticed when driving with my lights on ( because I have to since I work nights so it's always dark to and from work ) that my mpg is pretty bad. My girl friend always drives when there is light out in her prius so she seems to get about 2 mpg better then me all the time. Is there any way of improving this? I have a III so no LED lights. That would of came in handy for me. Anyone know of light bulbs that use less electric but still bright as the OEM?

I think it has to do with the way you drive, nothing to do with your lights being on.

[DaveinOlyWA]

in the Pri, anything that uses power will ultimately affect mileage so ya, the lights on will lower mileage.

look at a sprinter and a walker, both carrying a young child (well used analogy i know, but applicable). now whose perfomance is most affected? the sprinter of course, but he normally (when sprinting) is performing at or near his peak. the walker is not.

so look at the Pri as a sprinter, the walker as a gas car. the gas car uses the alternator to provide the power to the lights. the alternator, most of the time, puts out more power than the car actually needs. granted its metered so during lower power needs, it has less drag on engine, etc... but point is, it has potential to provide a LOT more power with a relatively minor effect on engine performance.

the Pri is just the opposite. it, by design, is set up to run as efficiently as possible. the problem; converting from high to low voltage is not efficient. so when the lights are on, more conversion, more loss, etc. is noticable since the Pri wastes less energy to begin with....

ok, now after all that...

many here have tried to measure the drop in mileage as have i, and i dont know of anyone here who has a measurable figure to give you.

i work 10 hour shifts and live north of most of the US. so i go from daylight both ways (about 3 weeks a year) to dark both ways ( during time change) to dark in morning only (most of the year) so...

i have attempted it 3-4 times and i have a lot of data but none of it really shows a distinct difference.

[fuzzy1]

Originally Posted by DBaum

I noticed when driving with my lights on ( because I have to since I work nights so it's always dark to and from work ) that my mpg is pretty bad. My girl friend always drives when there is light out in her prius so she seems to get about 2 mpg better then me all the time....

Any power consumption will decrease MPG, but the effect of lights should be tiny. The day vs. night temperature difference ought to have a larger impact. And differences in driving conditions and style will swamp even that.

I leave my lights on fulltime.

[Texas911]

Umm, guys, I know we want the best gas mileage but don't start driving with your lights off if you need them! Even in twilight, turn on your lights.