# Does Using Fog Lights/Other Electrical Accesories On Your Car Reduce Mileage Significantly? **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2011, 2:57am UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703 "2011-12-19T02:57:54Z")\ **Posts on this page:** 17\ **Page:** 4
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 22, 2011, 1:13pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/61 "2011-12-22T13:13:40Z")
> [@Throatwarbler\_Mangrove](#): > > OEM HIDs don’t blind anyone. Automotive lights are extremely tightly regulated by the relevant transportation authorities in every developed country and auto makers spend massive amounts of money making sure their lights don’t blind people. Just because it’s ‘extremely tightly regulated’ and ‘auto makers spend massive amounts of money making sure their lights don’t blind people.’ does not equate to OEM HIDs don’t blind anyone. That second one more speaks to that they do and the automakers are spending money to get them used anyway. HID lights are borderline just to make them passable, IIRC salts are used to alter the beam color just enough to make them pass. But anyway just because you are within the regulations (and just squeaking by to get in) do not mean you are not harming the vision of others. But all you need to do is face one oncoming and you know right away that they are way too bright and interfering with your ability to see the road too much. But like most things, throw enough money in the right places and you can make anything pass. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 22, 2011, 1:18pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/62 "2011-12-22T13:18:01Z")
Fog lights used to be mounted very low (lower then most cars go now), and IIRC the beam set forward (not down). The reason is that close to the ground there may be a fog free area due to the temperature of the ground interacting with the air, but this is pretty close to the ground. Most fog lights today are mounted far too high to take advantage of that so now they just light up the foreground area. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [December 22, 2011, 2:38pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/63 "2011-12-22T14:38:03Z")
> [@Muffin](#): > > Yes, those certainly are decorative only. I don’t think that means that the only real reason car maker include thims is aesthetics. Your car maker for your model, certainly yes. But there are others (such a mine), where they are functional as opposed to only being decorative. Mine too. People with Subarus definitely use their fog lights in real world situations, and mine work pretty well. ---
**Author:** ![Throatwarbler\_Mangrove](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@Throatwarbler\_Mangrove](https://boards.straightdope.com/u/Throatwarbler_Mangrove)\ **Post date:** [December 22, 2011, 3:59pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/64 "2011-12-22T15:59:32Z")
> [@kanicbird](#): > > Just because it’s ‘extremely tightly regulated’ and ‘auto makers spend massive amounts of money making sure their lights don’t blind people.’ does not equate to OEM HIDs don’t blind anyone. That second one more speaks to that they do and the automakers are spending money to get them used anyway. > > HID lights are borderline just to make them passable, IIRC salts are used to alter the beam color just enough to make them pass. But anyway just because you are within the regulations (and just squeaking by to get in) do not mean you are not harming the vision of others. HIDs appear to be glaring to others due to the nature of the lightsource. They actually do not affect the ability of other drivers to see the road. [http://deepblue.lib.umich.edu/bitstream/2027.42/49407/1/UMTRI-99-36.pdf](http://deepblue.lib.umich.edu/bitstream/2027.42/49407/1/UMTRI-99-36.pdf) > [@](#): > > Summary and Conclusions > Subjects were presented with glare stimuli that varied in size (0.3 or 0.6 degrees of visual > angle) and spectral power distribution (TH or HID). Discomfort glare was measured by > numerical ratings of subjective discomfort. Disability glare was measured by determining the > luminance threshold for detecting a pedestrian silhouette presented near the glare source. > Spectral power distribution affected discomfort glare, although, in contrast to previous studies > which had shown small but statistically significant effects, size did not affect discomfort glare. > The HID stimuli evoked higher estimates of discomfort than the TH stimuli, as expected from > previous research. Neither size nor spectral power distribution affected disability glare. > These results indicate that, for size and spectral power distribution, effects on discomfort > glare do not necessarily imply effects on disability glare. One would expect there to be cases > like this because the mechanisms of discomfort glare are believed to be much more complex than > the mechanisms of disability glare. Discomfort glare is therefore more likely to be sensitive to a > wide range of variables that are not likely to affect actual seeing ability, such as the difficulty of > a concurrent task (Sivak et al., 1991) or the range of stimuli presented (Olson & Sivak, 1983). > The fact that small, high-intensity discharge lamps do not seem to cause any special problems > with disability glare under the conditions of this experiment is encouraging, particularly because > disability glare is likely to have greater effects on safety than discomfort glare. > [@](#): > > But all you need to do is face one oncoming and you know right away that they are way too bright and interfering with your ability to see the road too much. But like most things, throw enough money in the right places and you can make anything pass. Before I understood the issue I also thought this way - the smaller “poiont” of the lightsource gave the impression of being brighter and the different appearance of HIDs had a psychosomatic effect where I thought they affected me more simply because I remembered them because they were different. Now that I am conscious of it HID lights no longer bother me and my ability to see was never affected. ---
**Author:** ![phreesh](https://avatars.discourse-cdn.com/v4/letter/p/9fc29f/32.png) [@phreesh](https://boards.straightdope.com/u/phreesh)\ **Post date:** [December 22, 2011, 4:18pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/65 "2011-12-22T16:18:56Z")
> [@lazybratsche](#): > > I agree that it’s probably negligible. But for the hell of it, here’s some back of the envelope figures: > > From Wikipedia, headlights seem to consume around 50 watts. Times two, and that’s 100 watts which makes the math easy. So to run your headlights for an hour, you need 0.1 kW \* h. > > Gasoline has an energy density of 37 kWh/gallon. By WAG, let’s say that the energy is converted into electrical power at around 20% efficiency (25% for engine, 80% for alternator sounds reasonable). So your hour of headlight use burns 0.5 kWh worth of gasoline, or around .5/37 ~ 0.02 gallons (rounding up for pessimism’s sake). > > Now, your car gets somewhere around 15 mpg in the city. I’ll assume city driving averages 20 mph (including all the time spent stopped) so you consume ~1.33 gallons per hour. Adding headlights, you consume 1.35 gallons per hour. Converting that back to mpg, 20 mph / (1.35 gallons/hour) = 14.8 mpg. > > That difference is probably measurable under controlled conditions, but is otherwise negligible. Especially compared to the less-than-fuel-efficient driving habits that are encouraged by such a car… Just wanted to say that this was an awesome answer. Great job. Also wanted to note that I am in the 'fog lights on a non-foggy day are annoying." Do they annoy other drivers? Yes. Yes they do. Do they blind other drivers? Yes. Yes they do. Do they improve long-range visibility? No they don’t. That’s not opinion. That’s science. Do they look kind of badass? Yeah. Yeah they do. Still, please don’t turn them on unless its foggy/snowy. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 22, 2011, 4:59pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/66 "2011-12-22T16:59:34Z")
> [@Throatwarbler\_Mangrove](#): > > HIDs appear to be glaring to others due to the nature of the lightsource. They actually do not affect the ability of other drivers to see the road. > > [http://deepblue.lib.umich.edu/bitstream/2027.42/49407/1/UMTRI-99-36.pdf](http://deepblue.lib.umich.edu/bitstream/2027.42/49407/1/UMTRI-99-36.pdf) Just want to point out that BMW and some others with a vested interest in allowing HID lighting helped sponsor this study, which goes to my point, spending a lot of money on such things is more of a indicator that they are trying to get something to stay approved when it perhaps should not be. > [@](#): > > Before I understood the issue I also thought this way - the smaller “poiont” of the lightsource gave the impression of being brighter and the different appearance of HIDs had a psychosomatic effect where I thought they affected me more simply because I remembered them because they were different. Now that I am conscious of it HID lights no longer bother me and my ability to see was never affected. So are you doubting that a brighter light source can effect night vision then a dimmer one? IIRC HID lamps put out far more light, so much that they use up a lot to light up the foreground because they are right at their limit max allowable down road light. But not only do you have someone right at the max limit shining light at you, but vastly lit ground around them. ---
**Author:** ![Throatwarbler\_Mangrove](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@Throatwarbler\_Mangrove](https://boards.straightdope.com/u/Throatwarbler_Mangrove)\ **Post date:** [December 22, 2011, 5:22pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/67 "2011-12-22T17:22:28Z")
> [@kanicbird](#): > > Just want to point out that BMW and some others with a vested interest in allowing HID lighting helped sponsor this study, which goes to my point, spending a lot of money on such things is more of a indicator that they are trying to get something to stay approved when it perhaps should not be. BMW is not a manufacturer of lights, the manufacturers of HID lights are mostly the same companies that also make all the other kinds of lights too. When I say “spend a lot of money” I mean they spend a lot of money researching and producing lighting equipment that meets all regulations in all major countries which is actually really hard. Small companies like Ferrari and whatnot often have to use off the shelf light units from other cars because they can’t justify the huge expense of designing unique lights for small production runs. You are suggesting that all the regulatory authorities in the EU, US, Japan, all over the world are being paid off by “Big Headlight” to approve unsafe headlights and have been getting away with it for 25+ years. > [@](#): > > So are you doubting that a brighter light source can effect night vision then a dimmer one? IIRC HID lamps put out far more light, so much that they use up a lot to light up the foreground because they are right at their limit max allowable down road light. But not only do you have someone right at the max limit shining light at you, but vastly lit ground around them. There are more factors that must be considered than just how bright a light is? If we’ve learned anything in this thread I should think it would be that where the light is aimed is more important than how bright the light is. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 22, 2011, 6:17pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/68 "2011-12-22T18:17:57Z")
> [@Throatwarbler\_Mangrove](#): > > BMW is not a manufacturer of lights, the manufacturers of HID lights are mostly the same companies that also make all the other kinds of lights too. When I say “spend a lot of money” I mean they spend a lot of money researching and producing lighting equipment that meets all regulations in all major countries which is actually really hard. Small companies like Ferrari and whatnot often have to use off the shelf light units from other cars because they can’t justify the huge expense of designing unique lights for small production runs. BMW has a vested interest in having the option of unique lighting that others will not be having (such as Ferrari). They don’t have to be a manufacturer to benefit. > [@](#): > > You are suggesting that all the regulatory authorities in the EU, US, Japan, all over the world are being paid off by “Big Headlight” to approve unsafe headlights and have been getting away with it for 25+ years. Do you have any doubt that regulations are sometimes influenced by people with vested interest? > [@](#): > > There are more factors that must be considered than just how bright a light is? If we’ve learned anything in this thread I should think it would be that where the light is aimed is more important than how bright the light is. We know that a small (less then 1 watt I think) handheld laser has been know to cause problems with airplane pilots, so yes a lot as to do with how much light reaches your eyes and what pattern so how it is aimed is important. Reflected light off the ground also reaches the eyes however, reflect enough and it will have a effect. HID lamps seem to surpass that level in many people as evidence by the number of complaints and I believe they are banned in certain countries. ---
**Author:** ![Throatwarbler\_Mangrove](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@Throatwarbler\_Mangrove](https://boards.straightdope.com/u/Throatwarbler_Mangrove)\ **Post date:** [December 22, 2011, 7:03pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/69 "2011-12-22T19:03:51Z")
> [@kanicbird](#): > > Do you have any doubt that regulations are sometimes influenced by people with vested interest? This is a tiresome argument. Sure, anything is possible, but I’ll leave to the reader to determine how plausible your suggestion is vs other likely explanations. > [@](#): > > We know that a small (less then 1 watt I think) handheld laser has been know to cause problems with airplane pilots, so yes a lot as to do with how much light reaches your eyes and what pattern so how it is aimed is important. Reflected light off the ground also reaches the eyes however, reflect enough and it will have a effect. HID lamps seem to surpass that level in many people as evidence by the number of complaints and I believe they are banned in certain countries. Which country? ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 22, 2011, 7:34pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/70 "2011-12-22T19:34:29Z")
> [@kanicbird](#): > > We know that a small (less then 1 watt I think) handheld laser has been know to cause problems with airplane pilots, so yes a lot as to do with how much light reaches your eyes and what pattern so how it is aimed is important. Reflected light off the ground also reaches the eyes however, reflect enough and it will have a effect. HID lamps seem to surpass that level in many people as evidence by the number of complaints and I believe they are banned in certain countries. I don’t know of any places where HIDs are outright banned, but in many/most countries (U.S. included) it’s illegal to put an HID capsule in a housing designed for an incandescent bulb. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [December 22, 2011, 9:31pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/71 "2011-12-22T21:31:46Z")
I see cars with HID all the time. You can’t miss them, but not so much because they’re a lot brighter, like high beams, but becuse they’re much more brilliant and white, like florescent light. And I’ve never found them to be blinding like high beams either. The ones that are must be HID elements in incandescent fixtures. Do they just fit into sockets they weren’t designed for? Because I would think they’d be different to specifically avoid this from happening. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 22, 2011, 9:36pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/72 "2011-12-22T21:36:24Z")
> [@Hail\_Ants](#): > > I see cars with HID all the time. You can’t miss them, but not so much because they’re a lot brighter, like high beams, but becuse they’re much more brilliant and white, like florescent light. And I’ve never found them to be blinding like high beams either. The ones that are must be HID elements in incandescent fixtures. Do they just fit into sockets they weren’t designed for? Because I would think they’d be different to specifically avoid this from happening. you can get dodgy aftermarket kits which bung HID capsules onto a base which fits into an existing housing. Typically they come with cheap poorly shielded ballasts which wipe out your radio reception and can negatively affect other electronic modules. People who put these things into their cars should be beaten with reeds. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 22, 2011, 10:04pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/73 "2011-12-22T22:04:46Z")
> [@jz78817](#): > > I don’t know of any places where HIDs are outright banned, but in many/most countries (U.S. included) it’s illegal to put an HID capsule in a housing designed for an incandescent bulb. Yeah I guess not, I though they were. I did notice the different design between European and US (NA) headlamp requirements, in particular that the European requirement is that no light goes in a ‘upward’ direction and HID lights need a cleaning system and auto levelers all to prevent blinding oncoming traffic. NA standards require some light ‘upward’ and have no requirement for the cleaning or leveling system. ---
**Author:** ![Anachronism](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@Anachronism](https://boards.straightdope.com/u/Anachronism)\ **Post date:** [December 23, 2011, 3:00am UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/74 "2011-12-23T03:00:05Z")
> [@Hail\_Ants](#): > > I see cars with HID all the time. You can’t miss them, but not so much because they’re a lot brighter, like high beams, but becuse they’re much more brilliant and white, like florescent light. And I’ve never found them to be blinding like high beams either. The ones that are must be HID elements in incandescent fixtures. Do they just fit into sockets they weren’t designed for? Because I would think they’d be different to specifically avoid this from happening. There are inexpensive (less than $100) aftermarket HID kits that will replace most regular bulbs. They are usually blinding to other drivers in a ‘regular’ reflector type headlight - something to do with the filament running in a different direction as I understand it. In a car with projector style headlights HIDs may be able to be swapped in without blinding other drivers but, as others have mentioned, it is illegal to put HIDs in a non HID housing. Also there are claims that using HID bulbs in a projector style housing provides worse light output, even if it is not blinding to other drivers, I am sure someone will provide the link. If you ever see a civic or other inexpensive car with what are obviously HIDs chances are it’s an aftermarket kit. Chances are they are blinding everyone coming towards them too. I have never felt blinded by OEM HIDs. I read somewhere that there where a large number of complaints about lights being ‘blinding’ to oncoming drivers when electrical systems went from 6 to 12 volts but I can’t find any sites. ---
**Author:** ![Anachronism](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@Anachronism](https://boards.straightdope.com/u/Anachronism)\ **Post date:** [December 23, 2011, 5:23pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/75 "2011-12-23T17:23:45Z")
Nobody? OK Here – [http://www.danielsternlighting.com/tech/bulbs/Hid/conversions/conversions.html](http://www.danielsternlighting.com/tech/bulbs/Hid/conversions/conversions.html) ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 23, 2011, 5:49pm UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/76 "2011-12-23T17:49:35Z")
I already linked to Stern’s site in my first post in this thread. ---
**Author:** ![Nunzio\_Tavulari](https://avatars.discourse-cdn.com/v4/letter/n/b9bd4f/32.png) [@Nunzio\_Tavulari](https://boards.straightdope.com/u/Nunzio_Tavulari)\ **Post date:** [December 24, 2011, 3:57am UTC](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703/77 "2011-12-24T03:57:54Z")
> [@Hail\_Ants](#): > > But mostly, they just look nice. And they have no effect on oncoming traffic, they’re not bright enough. All of the auxiliary light bulbs that I’ve seen in cars a decade old or less use 55 watt bulbs. That’s the same wattage as a low beam headlight. I’m not confident that engineers spent as more time worrying about the beam pattern on the luxe lights as they did on the headlights. Most are decorative only and not “true” fog lights as the OP has claimed. I have been distracted by auxiliary lights on approaching vehicles but in most cases they were on trucks and SUVS. Those have a higher ride height than autos and I have a low slung car that puts my head at the level of most sedan driver’s shoulders. Please. If it’s not foggy, don’t use your fog lights. No, they don’t make you more visible than your two headlights already do. Some lighting configurations obscure the outline of your vehicle. Is that a jacked-up truck with a sports car behind it? Are those three lights a motorcycle and a car or just a car with one light out? Some manufacturers put lights where they look cool, which can make it difficult to see your turn signals from certain angles. [Previous page](https://boards.straightdope.com/t/does-using-fog-lights-other-electrical-accesories-on-your-car-reduce-mileage-significantly/606703.md?page=3)