Effects of Headlights on mpg: 6%?

[cons]

This guy claims you can generally save around 6% of gas by not having your lights on. If true, I think using LED lights, and taking off the AC and/or alternator would really make a huge difference. I don't really see many ecomodders here reporting about this move so I'm curious what the thoughts are about this. Also, have people figured out the drag of having all your windows down vs. up? I don't have a scan-guage to do this and don't want to waste a tank trying.

Is the alternator always running and being a drain, or is it on an as needed basis?

Driving with your Headlights On

Also, better to use the windows down to cool off or a fan? Does the fan drain the FE or is it going anyway?

[RobertSmalls]

The corner lights and dash lights draw about 90W, and headlights draw 110W according to my own measurements. For a 50% efficient alternator, that's an additional 400W (0.5HP) at the crank.

I've run the numbers through our calculator for a hypothetical Honda Insight in which someone installed a 50% efficient alternator. This car has a larger than typical percentage MPG hit when turning on the headlights, because it spends relatively little energy on aerodynamic drag and rolling resistance.

With a 200W electrical load (ECU, fuel pump, etc.) creating a 400W load at the crank, you'd get about 70.13mpg @ 65mph. Turn on the lights, and you get 67.10mpg @ 65mph. 4% difference.

Lights off
Lights on

The percentage difference in a Ranger is much, much smaller, but the fact that you save about 0.04gal/hour is constant. No matter what you're driving, you can save the same amount of fuel by turning off unneeded 12V loads.

Windows up, fans on is much more efficient in my car than windows down, fans off.

[tumnasgt]

I use my lights all the time, with the theory that if people see me better, they are less likely to pull out in front of me (especially in winter here, there are so many shadows it's easy to miss a car without lights), saving me from slamming on the brakes.

I have considered getting LED DRLs, but when I last looked, they are about $150-250US for a brand name set, and I don't drive all that much, so the payback time would be quite long.
LED bulbs are fine for things like taillights and position markers, but for headlights they just aren't bright enough (with some special exceptions). Some new cars have LED dipped-beams, but you can't retrofit them to cars easily as the beam from LEDs isn't the same as a halogen's.

[cfg83]

cons -

I disabled my DRL's because they were drawing maybe 10 Amps (10 Amps*12 Volts = 120 Watts) minimum for both headlight bulbs. In my Saturn S-Series, my DRLs are my high-beams (running at lower Amps?!?!?!). I delay using my headlights. At sunset I have my driving lights on, which are about 80% LED at this point.

I also have other ways of "being seen" and I categorically recommend MetroMPG's safety thread :

http://ecomodder.com/forum/showthrea...ded-13781.html

I especially recommend post #12 :

3) Extra communication with following drivers: when warranted, repeatedly flash your brake lights, or turn on your 4-ways - I always do this on the freeway when I spot a significant slowdown ahead. This applies when stopping or already stopped.

(Some Mercedes cars automatically activate a special high-intensity - possibly flashing, I'm not sure - brake lights when the driver brakes harder than usual.)

I pretty much do this anytime I see bad stuff up ahead and/or I am reacting to an emergency situation. It sometimes makes my passengers nervous, but I explain and they understand my intentions.

CarloSW2

[Arragonis]

I have xenon headlights and like others run with them on full time except in sunny weather as only the blind it seems are allowed to drive in Edinburgh

I haven't noticed any significant drag on using them vs not in summer when it isn't raining. My engine has a pretty heavy flywheel though so I don't think the load of the lights makes much difference.

My SG2 LOD and GPH do not change at idle lights on or off.

[alvaro84]

I can't turn Teresa's low-beam light off (constant 55W load) - because of regulations the light just doesn't have a switch (AFAIK lighting on motorcycles is compulsory in Europe, every time) - but I think I normally would seldom turn it off anyway. According to my experience I'm practically invisible without it
It would be nice to see a LED replacement for H3 halogene though - something that's at least as bright as the incandescent version (and lights the same angle - though it depends on the optics of the headlight too).
My backlight and instrument panel lights are already replaced with LEDs.

[basjoos]

On the aerocivic, turning on the headlights knocks the mileage down by 2 to 3 mpg. On the F150, lights on or off has no noticable effect on mileage.

On the aerocivic at any speed over 30mph, windows closed/fan on nets better mileage than windows open/fan off. On the F150, the mileage effects of windows open/closed or fan on/off is unnoticeable above the high levels of background drag.

[euromodder]

Originally Posted by cons

This guy claims you can generally save around 6% of gas by not having your lights on.

Though there will be a minor power drain from using the headlights, I've never noticed any perceptible difference in FE with or without having my headlights on (either as DRL of as normal lights).

I had Volvo's always-on set-up changed to be able to switch the headlights off, but not because of FE reasons

If true, I think using LED lights

Nothing else should really be used for DRL.

LEDs draw a lot less power, and being smaller they're sufficiently different from regular headlights to minimize the risk of other road users being rendered nearly invisible near cars with them on.

Originally Posted by alvaro84

I can't turn Teresa's low-beam light off (constant 55W load) - because of regulations the light just doesn't have a switch (AFAIK lighting on motorcycles is compulsory in Europe, every time) - but I think I normally would seldom turn it off anyway. According to my experience I'm practically invisible without it

AFAIK only in the UK it's not mandatory to have your headlight on on a m/c .

Don't turn it off for FE reasons on a m/c.
It's bad enough with the headlight on, no need to make it even more dangerous.

If it's allowed where you live, try out a yellow light.

[alvaro84]

Oh, I thought it is compulsory everywhere in the EU, because it is in Hungary and the Germans made Teresa this way. I was wrong then.
No, I don't turn it off (I can't do it to begin with) - but it went out once, riding on the main road 4 of Hungary (2 lanes with pretty heavy traffic). And yes, it was pretty dangerous, several drivers started overtaking heading towards me in my lane, sometimes I had to flee to the (paved, thankfully) shoulder of the road. I replaced the bulb immediately when I got what was wrong. (There's no law to carry spare bulbs anymore here, yet I do - and I don't regret it...) Especially that we got home at night, so having a lowbeam was crucial...

[Daox]

An alternator delete will reduce electrical loads completely. You of course are still using power that you have to pay for at the wall, but at least its not coming from oil.