It's right for the night...
Discussion
...Thousands of lights show us the way.
I thought I'd jot down a few thoughts on night driving now summer has ended and the nights are starting to draw in a bit. Its not an excessively complicated subject if I'm being honest, so once again, my apologies to anyone who finds this post patronising or simplistic in any way, but as per usual, it's aimed at all levels of driver, so feel free to take what you want and leave what you don't.
There's nothing inherently dangerous or excessively risky about driving at night. We're lucky to live in a highly developed country with a relatively high proportion of well lit roads, particularly in urban and suburban areas. Having said that, there are still many thousands of miles of unlit roads in between our towns and cities, but most modern cars have excellent lights and our annual MOT tests mean that most cars have defective bulbs replaced once a year at a minimum.
We also have many laws and regulations which govern what lights can or cannot be fitted to vehicles, how they must be maintained, and even when they must be switched on and off.
I know this doesn't sound particularly advanced, but next time you're abroad - even in countries which are considered as advanced as ours - try driving at night and you'll immediately notice the difference - both in the quality and quantity of street lighting, and in the maintenance and use of headlights. Go a little further afield and the differences are even more noticable. I once had the misfortune of travelling in a taxi in Egypt at night. I don't think I saw more than three or four other cars with headlights on for the entire journey. Everyone simply drove at night with no lights whatsoever. Horns were a different story - they were used constantly, but headlights or sidelights? No. I tried asking the driver why no-one uses their lights, but he just shouted "baksheesh", which suggested he would,have put them on if I'd have tipped him more.
Anyway, on to the driving tips. At the risk of sounding like I'm teaching you to suck eggs, there are two key things to remember when driving at night...
(1) It's more difficult to see.
(2) It's more difficult for others to see you.
Although there are a couple of advantages to visibility at night which we'll look at in a bit.
To help with both of these issues, car manufacturers fit a variety of different lights to their cars, so we'll start with a brief look at the legalities of driving at night.
Drivers must use sidelights between sunset and sunrise.
Additionally, drivers must use (dipped) headlights during the hours of darkness (half-an-hour after sunset until half-an-hour before sunrise),except when using a road which has lit street lighting, in which case the only legal requirement is to use sidelights.
Its also a legal requirement to use headlights when visibility is seriously reduced (generally when, due to weather conditions or perhaps smoke, visibility is reduced to less than 100 metres).
Note that there is no legal requirement to use foglights when visibility is seriously reduced. The legislation outlines when you should not use foglights, but there is no law which states that you have to use them.
There is a lot more to the legislation, but for most car drivers, thats all you need to know.
On to the actual driving.
Although the legislation only requires sidelights at night in built-up areas, bearing in mind item (2) above, I can see no logical reason why you would not choose to used dipped beam headlights at all times when its dark. Even on an older car with weaker headlights, dipped beam lights make your vehicle much more visible to other road users, so my advice is to use dipped beam headlights at all times when you're driving at night and save the sidelights for parking.
One thing to be careful of here - some car manufacturers, Vauxhall for instance, have an annoying habit of designing cars with instrument binnacles which light up night and day when the ignition is switched on, irrespective of whether the lights are switched on or not. It's very easy, particularly if you're in a well-lit area at night, to get in one of these cars, see the dashboard light up, assume the lights are on and drive off into the gloom, wondering why everyone is flashing at you. I did it myself a few times when the police panda fleet was updated about 10 years ago. You're less likely to do it if your own car has this feature, because we all tend to know our own cars well, but always look for the green symbol on the dash to confirm your lights are on.
So, built-up areas, street lights etc - there's not a lot to say really. Leave your headlights on dipped beam, position yourself generally towards the centre of the road to allow vehicles approaching junctions to your left to get a slightly earlier view of you and try to go handbrake-neutral when you're stationary as modern brake lights can be very dazzling to drivers behind.
Many vehicles these days - my own included - are fitted with automatic headlights. Just flick the light switch to the "A" setting and the car monitors how light or dark it is and switches the lights on and off as appropriate. They are generally good systems and I use mine, but there are a couple of things to bear in mind.
Firstly, they will come on during the day if you enter a tunnel. This is generally a good thing, but can be misinterpreted by other drivers as a headlight flash, so keep a careful eye on the drivers around you and expect the occasional lane change.
Secondly, be careful if you lend your car to someone else, or if it goes in for service. Its easy to take automatic lights for granted (mine never move from the "A" position), and then be caught out if someone else uses your car and switches them off.
A note on courtesy. It seems to be a well established tradition in this country that drivers acknowledge a courtesy by flashing their headlights. Personally, I can't think of a worse way to thank someone than by burning their retinas out and leaving them temporarily partially blinded. You wouldn't thank someone for buying you a pint by poking them in the eyes, would you? I know a "thank you" wave isn't really visible at night, so my preference is to momentarily turn my lights from dipped-beam to sidelights and then back to dipped-beam again. It will acknowledge a courtesy from an oncoming driver without causing them to drive into the nearest bus shelter.
On unlit rural roads, there is much more to think about when it comes to lighting. The priority moves from being seen, to being able to see, and this is where you need to make use - by which I mean intelligent use - of your "main", "high" or "full" beam headlights.
If you are on an unlit road and there are no vehicles in front, use your main beam. It will illuminate the road much further ahead and allow a planned approach to hazards. It also simplifies a couple of roadcraft principles. The overriding safety principle is that you should always be able to stop on your own side of the road in the distance you can see to be clear. At night, on an unlit road, this principle is easy to apply because the distance you can see to be clear is never any further than the distance illuminated by your headlights.
The second principle it simplifies is that of assessing the correct speed to take a corner using the limit point. The limit point is the furthest point in a corner in which you have an uninterrupted view of the road surface. At night, on an unlit road, this is the furthest point in a corner which is illuminated by your headlights.
If I ever had a student who struggled with limit points, I would try to take them out in the dark, after which they seemed to "get" it.
If you can see the headlights or tail lights of a car ahead, you should switch your lights to dipped beam. The principle is that if you can see their lights, they can see yours and you really don't want to dazzle the driver of a vehicle which is travelling towards you at speed.
There is usually no need to dip your lights before you see headlights or tail lights. Many people dip their lights when they see the "halo" of oncoming vehicles but this isn't usually necessary. Some people get quite nippy about it too. I often see the halos of oncoming cars furiously flashing their lights at me before Their lights actually come into view. I always dip at the appropriate point, of course, but its amusing to see how upset some people get before you've even done anything wrong.
The exception with this point is for large goods vehicles with a raised driving position. These vehicles have headlights fitted at normal height but the driver sits higher up, so it is possible to dazzle them even if you can't see their headlights, so dip early if you think it's an HGV approaching.
If I'm on an unlit road at night, using main beam, I don't generally dip my lights if I see a vehicle approaching a junction to the left or right. Over the years, I have found that dipping lights under these circumstances can be misunderstood by the vehicles in the junction as a signal to pull out. People are much less likely to pull out in front of a vehicle with high beam displayed than one which has just dipped its lights. You won't find this in a textbook anywhere - its just based on my own observations. It might seem a little inconsiderate to dazzle a car in a junction, but they can look away and you can also usually pick out the driver and observe their actions better if your lights remain on high beam. If the vehicle pulls out regardless then, of course, dip your lights.
If you are dazzled by an oncoming vehicle, whats the best course of action? Its very tempting to give them a taste of their own medicine and burn out their retinas, but do you really want two partially-blinded drivers driving towards each other at speed?
The best advice is to look slightly away from the headlights. Shining a bright light into your eyes creates a "flash blindness" which is a sort of blob of blindness in one part of your eye, similar to when a camera flash goes off. This flash spot can remain for a few seconds or minutes, so its best to look away slightly from the lights so that your flash blindness occurrs in an area outside your main field of vision. Try to look to the left of the oncoming car - towards the nearside kerb.
If you want to indicate to the oncoming vehicle that they are a main beam numpty, try my courtesy signal of switching to sidelights a couple of times. This will flash your lights without causing excessive dazzle and might wake them up.
If the car behind is the problem, almost all cars are fitted with dipping rear-view mirrors which dim the appearance of following traffic. If you're a company director type, you may even have an automatic dipping mirror, but for most of us mere mortals, the mirror can be dipped by flicking the lever underneath the mirror, or in the case of BMWs, turning the red alarm light under the mirror.
When overtaking, keep your lights on dipped beam until the front of your car has passed the door mirrors of the overtaken car - or the frontmost overtaken car if you're overtaking multiple vehicles.
If you are being overtaken, or you think the car behind wants to overtake, help them out by keeping your main beam on until their door mirrors have passed the front of your car, then dip your lights.
The "halo" I mentioned earlier is one of the biggest advantages of driving at night. During the day, your view is limited by hedges, trees, buildings etc, but at night, the halo of headlights can give you a very clear indication as to which direction the road is going and how severe the corners ahead are.
The only downside to using main beam on modern unlit roads is that road signs these days seem to be much more reflective than they used to be. So much so that I sometimes find that I have to dip my headlights as I get closer to some signs to avoid being blinded by tne reflection of my own headlights.
There's progress for you.
I thought I'd jot down a few thoughts on night driving now summer has ended and the nights are starting to draw in a bit. Its not an excessively complicated subject if I'm being honest, so once again, my apologies to anyone who finds this post patronising or simplistic in any way, but as per usual, it's aimed at all levels of driver, so feel free to take what you want and leave what you don't.
There's nothing inherently dangerous or excessively risky about driving at night. We're lucky to live in a highly developed country with a relatively high proportion of well lit roads, particularly in urban and suburban areas. Having said that, there are still many thousands of miles of unlit roads in between our towns and cities, but most modern cars have excellent lights and our annual MOT tests mean that most cars have defective bulbs replaced once a year at a minimum.
We also have many laws and regulations which govern what lights can or cannot be fitted to vehicles, how they must be maintained, and even when they must be switched on and off.
I know this doesn't sound particularly advanced, but next time you're abroad - even in countries which are considered as advanced as ours - try driving at night and you'll immediately notice the difference - both in the quality and quantity of street lighting, and in the maintenance and use of headlights. Go a little further afield and the differences are even more noticable. I once had the misfortune of travelling in a taxi in Egypt at night. I don't think I saw more than three or four other cars with headlights on for the entire journey. Everyone simply drove at night with no lights whatsoever. Horns were a different story - they were used constantly, but headlights or sidelights? No. I tried asking the driver why no-one uses their lights, but he just shouted "baksheesh", which suggested he would,have put them on if I'd have tipped him more.
Anyway, on to the driving tips. At the risk of sounding like I'm teaching you to suck eggs, there are two key things to remember when driving at night...
(1) It's more difficult to see.
(2) It's more difficult for others to see you.
Although there are a couple of advantages to visibility at night which we'll look at in a bit.
To help with both of these issues, car manufacturers fit a variety of different lights to their cars, so we'll start with a brief look at the legalities of driving at night.
Drivers must use sidelights between sunset and sunrise.
Additionally, drivers must use (dipped) headlights during the hours of darkness (half-an-hour after sunset until half-an-hour before sunrise),except when using a road which has lit street lighting, in which case the only legal requirement is to use sidelights.
Its also a legal requirement to use headlights when visibility is seriously reduced (generally when, due to weather conditions or perhaps smoke, visibility is reduced to less than 100 metres).
Note that there is no legal requirement to use foglights when visibility is seriously reduced. The legislation outlines when you should not use foglights, but there is no law which states that you have to use them.
There is a lot more to the legislation, but for most car drivers, thats all you need to know.
On to the actual driving.
Although the legislation only requires sidelights at night in built-up areas, bearing in mind item (2) above, I can see no logical reason why you would not choose to used dipped beam headlights at all times when its dark. Even on an older car with weaker headlights, dipped beam lights make your vehicle much more visible to other road users, so my advice is to use dipped beam headlights at all times when you're driving at night and save the sidelights for parking.
One thing to be careful of here - some car manufacturers, Vauxhall for instance, have an annoying habit of designing cars with instrument binnacles which light up night and day when the ignition is switched on, irrespective of whether the lights are switched on or not. It's very easy, particularly if you're in a well-lit area at night, to get in one of these cars, see the dashboard light up, assume the lights are on and drive off into the gloom, wondering why everyone is flashing at you. I did it myself a few times when the police panda fleet was updated about 10 years ago. You're less likely to do it if your own car has this feature, because we all tend to know our own cars well, but always look for the green symbol on the dash to confirm your lights are on.
So, built-up areas, street lights etc - there's not a lot to say really. Leave your headlights on dipped beam, position yourself generally towards the centre of the road to allow vehicles approaching junctions to your left to get a slightly earlier view of you and try to go handbrake-neutral when you're stationary as modern brake lights can be very dazzling to drivers behind.
Many vehicles these days - my own included - are fitted with automatic headlights. Just flick the light switch to the "A" setting and the car monitors how light or dark it is and switches the lights on and off as appropriate. They are generally good systems and I use mine, but there are a couple of things to bear in mind.
Firstly, they will come on during the day if you enter a tunnel. This is generally a good thing, but can be misinterpreted by other drivers as a headlight flash, so keep a careful eye on the drivers around you and expect the occasional lane change.
Secondly, be careful if you lend your car to someone else, or if it goes in for service. Its easy to take automatic lights for granted (mine never move from the "A" position), and then be caught out if someone else uses your car and switches them off.
A note on courtesy. It seems to be a well established tradition in this country that drivers acknowledge a courtesy by flashing their headlights. Personally, I can't think of a worse way to thank someone than by burning their retinas out and leaving them temporarily partially blinded. You wouldn't thank someone for buying you a pint by poking them in the eyes, would you? I know a "thank you" wave isn't really visible at night, so my preference is to momentarily turn my lights from dipped-beam to sidelights and then back to dipped-beam again. It will acknowledge a courtesy from an oncoming driver without causing them to drive into the nearest bus shelter.
On unlit rural roads, there is much more to think about when it comes to lighting. The priority moves from being seen, to being able to see, and this is where you need to make use - by which I mean intelligent use - of your "main", "high" or "full" beam headlights.
If you are on an unlit road and there are no vehicles in front, use your main beam. It will illuminate the road much further ahead and allow a planned approach to hazards. It also simplifies a couple of roadcraft principles. The overriding safety principle is that you should always be able to stop on your own side of the road in the distance you can see to be clear. At night, on an unlit road, this principle is easy to apply because the distance you can see to be clear is never any further than the distance illuminated by your headlights.
The second principle it simplifies is that of assessing the correct speed to take a corner using the limit point. The limit point is the furthest point in a corner in which you have an uninterrupted view of the road surface. At night, on an unlit road, this is the furthest point in a corner which is illuminated by your headlights.
If I ever had a student who struggled with limit points, I would try to take them out in the dark, after which they seemed to "get" it.
If you can see the headlights or tail lights of a car ahead, you should switch your lights to dipped beam. The principle is that if you can see their lights, they can see yours and you really don't want to dazzle the driver of a vehicle which is travelling towards you at speed.
There is usually no need to dip your lights before you see headlights or tail lights. Many people dip their lights when they see the "halo" of oncoming vehicles but this isn't usually necessary. Some people get quite nippy about it too. I often see the halos of oncoming cars furiously flashing their lights at me before Their lights actually come into view. I always dip at the appropriate point, of course, but its amusing to see how upset some people get before you've even done anything wrong.
The exception with this point is for large goods vehicles with a raised driving position. These vehicles have headlights fitted at normal height but the driver sits higher up, so it is possible to dazzle them even if you can't see their headlights, so dip early if you think it's an HGV approaching.
If I'm on an unlit road at night, using main beam, I don't generally dip my lights if I see a vehicle approaching a junction to the left or right. Over the years, I have found that dipping lights under these circumstances can be misunderstood by the vehicles in the junction as a signal to pull out. People are much less likely to pull out in front of a vehicle with high beam displayed than one which has just dipped its lights. You won't find this in a textbook anywhere - its just based on my own observations. It might seem a little inconsiderate to dazzle a car in a junction, but they can look away and you can also usually pick out the driver and observe their actions better if your lights remain on high beam. If the vehicle pulls out regardless then, of course, dip your lights.
If you are dazzled by an oncoming vehicle, whats the best course of action? Its very tempting to give them a taste of their own medicine and burn out their retinas, but do you really want two partially-blinded drivers driving towards each other at speed?
The best advice is to look slightly away from the headlights. Shining a bright light into your eyes creates a "flash blindness" which is a sort of blob of blindness in one part of your eye, similar to when a camera flash goes off. This flash spot can remain for a few seconds or minutes, so its best to look away slightly from the lights so that your flash blindness occurrs in an area outside your main field of vision. Try to look to the left of the oncoming car - towards the nearside kerb.
If you want to indicate to the oncoming vehicle that they are a main beam numpty, try my courtesy signal of switching to sidelights a couple of times. This will flash your lights without causing excessive dazzle and might wake them up.
If the car behind is the problem, almost all cars are fitted with dipping rear-view mirrors which dim the appearance of following traffic. If you're a company director type, you may even have an automatic dipping mirror, but for most of us mere mortals, the mirror can be dipped by flicking the lever underneath the mirror, or in the case of BMWs, turning the red alarm light under the mirror.
When overtaking, keep your lights on dipped beam until the front of your car has passed the door mirrors of the overtaken car - or the frontmost overtaken car if you're overtaking multiple vehicles.
If you are being overtaken, or you think the car behind wants to overtake, help them out by keeping your main beam on until their door mirrors have passed the front of your car, then dip your lights.
The "halo" I mentioned earlier is one of the biggest advantages of driving at night. During the day, your view is limited by hedges, trees, buildings etc, but at night, the halo of headlights can give you a very clear indication as to which direction the road is going and how severe the corners ahead are.
The only downside to using main beam on modern unlit roads is that road signs these days seem to be much more reflective than they used to be. So much so that I sometimes find that I have to dip my headlights as I get closer to some signs to avoid being blinded by tne reflection of my own headlights.
There's progress for you.
R_U_LOCAL said:
most modern cars have excellent lights
road signs these days seem to be much more reflective than they used to be. So much so that I sometimes find that I have to dip my headlights as I get closer to some signs to avoid being blinded by tne reflection of my own headlights.
Manufacturers (IME) advertise "bigger, better and brighter headlights" on each new car. Perhaps they're getting to the point where they're too bright?road signs these days seem to be much more reflective than they used to be. So much so that I sometimes find that I have to dip my headlights as I get closer to some signs to avoid being blinded by tne reflection of my own headlights.
I find that dipped headlights on some approaching cars can be painfully bright. Obviously my eyes are getting older each day, but OTOH I have a regular eye test and don't require any correction yet.
Many modern cars have constant dash illumination, so at dusk many drivers are thinking their sidelights are on when they're not.
Another development - with led drls, on the front only, I see so many cars driving past sunset with front sidelights on and absolutely nothing at the rear - Priuses are a common one for this.
Surely manufacturers will address this pretty soon....?
Another development - with led drls, on the front only, I see so many cars driving past sunset with front sidelights on and absolutely nothing at the rear - Priuses are a common one for this.
Surely manufacturers will address this pretty soon....?
I would personally like to see manufactures get rid of side lights on the switch, too many people use then when conditions require dipped beam. Lights should be on or off when driving i.e. dipped beam and nothing in between, side lights are of no use to any one when driving and if they are needed when parking the dipped beam should revert to them when the ignition is off!
Any thought on the intelligent headlights that are now available as options on many new cars.
Didn't go for them on my Golf but 2 systems available
Basic - Normal is main beam. When it detects vehicle approaching, switches from main to dipped.
Top - Normal is main. When it detects vehicles approaching stays on main but bends the light away as not to dazzle driver.
Didn't go for them on my Golf but 2 systems available
Basic - Normal is main beam. When it detects vehicle approaching, switches from main to dipped.
Top - Normal is main. When it detects vehicles approaching stays on main but bends the light away as not to dazzle driver.
Rick101 said:
Any thought on the intelligent headlights that are now available as options on many new cars.
Didn't go for them on my Golf but 2 systems available
Basic - Normal is main beam. When it detects vehicle approaching, switches from main to dipped.
Top - Normal is main. When it detects vehicles approaching stays on main but bends the light away as not to dazzle driver.
I can't really comment myself as I'm yet to try these systems.Didn't go for them on my Golf but 2 systems available
Basic - Normal is main beam. When it detects vehicle approaching, switches from main to dipped.
Top - Normal is main. When it detects vehicles approaching stays on main but bends the light away as not to dazzle driver.
I've made the mistake of dismissing things like automatic lights and wipers in the past before getting a car with them fitted & changing my opinion, so I'll reserve comment on these systems until I try them.
I probably would have gone for them if I were keeping the car longer but it's a relatively short term lease so wasn't good value.
Regardless, I think the hardware is already installed as when starting the car as well as the usual height calibration you get with xenons, it also does a left/right sweep. This is probably for the cornering light function. Whilst I've not really noticed an massive benefit from cornering lights I have found in the setting menu an option to adjust beam for driving on the continent. That I was impressed with. Something I regularly do and now I don't have to faf about with stickers on my headlights!
Regardless, I think the hardware is already installed as when starting the car as well as the usual height calibration you get with xenons, it also does a left/right sweep. This is probably for the cornering light function. Whilst I've not really noticed an massive benefit from cornering lights I have found in the setting menu an option to adjust beam for driving on the continent. That I was impressed with. Something I regularly do and now I don't have to faf about with stickers on my headlights!
greygoose said:
It's a good point about signs being very bright, I have to turn off my main beam at a new sign every night as it is blindingly bright as you approach it, not sure what the coating on it is as all the other signs on the road don't react in the same way.
My HID-equipped Hella Driving lamps give the same problem -worth having them for the additional lighting on the back roads, though.
Just a note about dipping lights down rather than up to acknowledge somebody. I tried it this morning without success. I have xenon light and it takes about a second for them to reduce in brightness. I can flick the switch from dipped to sidelights and it makes no difference at all. YOu have to turn and hold it for about a second before seeing the light reduce.
Good tip but with more and more cars getting newer technology it's at risk of being outdated very quickly.
I've noticed that with a few things I've been taught, the tech available now often means the spiel that has worked for many years is now wrong.
Good tip but with more and more cars getting newer technology it's at risk of being outdated very quickly.
I've noticed that with a few things I've been taught, the tech available now often means the spiel that has worked for many years is now wrong.
Rick101 said:
Just a note about dipping lights down rather than up to acknowledge somebody. I tried it this morning without success. I have xenon light and it takes about a second for them to reduce in brightness. I can flick the switch from dipped to sidelights and it makes no difference at all. YOu have to turn and hold it for about a second before seeing the light reduce.
Good tip but with more and more cars getting newer technology it's at risk of being outdated very quickly.
I've noticed that with a few things I've been taught, the tech available now often means the spiel that has worked for many years is now wrong.
Good point - thank you.Good tip but with more and more cars getting newer technology it's at risk of being outdated very quickly.
I've noticed that with a few things I've been taught, the tech available now often means the spiel that has worked for many years is now wrong.
Perhaps a quick flash of the hazard lights? Or a brief on and off of the fog lights?
Anything really to acknowledge a courtesy without blinding the person you're thanking.
This topic normally generates outraged comments on the misuse of fog lights: front, rear or both! I hate the misuse of rear fogs but is there a more pointless feature on a modern car than front fog lights? In my experience they are all but useless as a means of illuminating the way ahead plus, of course, it is illegal to use them anyway in all but the very worst conditions. On my current company Vauxhall they are so useless that without checking the dash panel light it is almost literally impossible to tell if they are actually on or off. You certainly wouldn't want to rely on them in thick fog!
R_U_LOCAL said:
We're lucky to live in a highly developed country with a relatively high proportion of well lit roads, particularly in urban and suburban areas.
I would suggest that the effectiveness of well lit roads is diminishing with LED street lights replacing the sodium lamps. London Borough of Bromley, for example, is gradually moving over to LEDs as I understand they are more energy efficient. That may be, but they provide only a small area of downward direct light compared to the familiar 'glow' of the orange lighting and much detail is being lost. I now find night driving in these areas is much harder on the eyes due to the combination of low street lighting and brighter dipped beam headlights.
This surely has to be to the detriment of safe night driving?
There is a school of thought which suggests that a combination of front foglights and sidelights is most effective in thick fog. Even the legislation allows for this, giving an exemption from dipped headlights on non-30mph limit roads if its foggy & you're displaying a sidelight/foglight combination.
The problem with driving in fog is that any bright light you display to the front is reflected back at you by the fog itself (or by the tiny water droplets which make up fog if you want to be technical).
I used to spectate on a lot of stage rallies, and rally drivers will generally run with no lights at all in thick fog during the daytime because they find no lights gives them better visibility than any other combination of lights (and rally cars tend to have the most varied combinations of lights). On the road in fog, however, no lights isn't really an option because no-one can see you.
I've tried the sidelight/foglight combination in a number of cars and I've never really found it much better than just headlights, and I've often found it worse. The idea is that the low front foglights project a beam across the road surface, whilst the sidelights prevent excessive light reflection from the fog. Sounds good in theory, but it's not great in reality.
A note on intelligent use of foglights - many people see mist or fog and then just switch their foglights on as a sort of pavlovian response & leave them on for the rest of the journey. In reality, the occasions you actually need to use foglights are extremely limited. Visibility of less than 100 metres is extremely thick fog or very heavy snowfall (the only two weather conditions which would require high intensity foglight use) and those weather conditions are quite rare.
You don't need foglights when it's a bit misty, or there's a bit of dampnesss in the air, and you definitely never need them when its raining, no matter how torrentially, because the extra glare caused by foglights reflecting off a wet road create more dangers rather than less.
If you are driving in <100M visibility, your rear foglights are a priority to ensure traffic approaching from the rear can see you, but once you can see the headlights of following traffic in your mirror, it's usually best to switch off your foglights, because if you can see their headlights, they'll be able to see your tail lights without foglight assistance. Don't forget that rear foglights can mask your brake lights and make it more likely that a following vehicle will not see when you are slowing down.
Fog can be patchy too, so switch the fogs on just when they are needed and switch them off as soon as it's clear again.
And remember - they are foglights - NOT driving lamps, posing lamps or fashion accessories. If you're not in thick fog or snow, leave them switched off!
The problem with driving in fog is that any bright light you display to the front is reflected back at you by the fog itself (or by the tiny water droplets which make up fog if you want to be technical).
I used to spectate on a lot of stage rallies, and rally drivers will generally run with no lights at all in thick fog during the daytime because they find no lights gives them better visibility than any other combination of lights (and rally cars tend to have the most varied combinations of lights). On the road in fog, however, no lights isn't really an option because no-one can see you.
I've tried the sidelight/foglight combination in a number of cars and I've never really found it much better than just headlights, and I've often found it worse. The idea is that the low front foglights project a beam across the road surface, whilst the sidelights prevent excessive light reflection from the fog. Sounds good in theory, but it's not great in reality.
A note on intelligent use of foglights - many people see mist or fog and then just switch their foglights on as a sort of pavlovian response & leave them on for the rest of the journey. In reality, the occasions you actually need to use foglights are extremely limited. Visibility of less than 100 metres is extremely thick fog or very heavy snowfall (the only two weather conditions which would require high intensity foglight use) and those weather conditions are quite rare.
You don't need foglights when it's a bit misty, or there's a bit of dampnesss in the air, and you definitely never need them when its raining, no matter how torrentially, because the extra glare caused by foglights reflecting off a wet road create more dangers rather than less.
If you are driving in <100M visibility, your rear foglights are a priority to ensure traffic approaching from the rear can see you, but once you can see the headlights of following traffic in your mirror, it's usually best to switch off your foglights, because if you can see their headlights, they'll be able to see your tail lights without foglight assistance. Don't forget that rear foglights can mask your brake lights and make it more likely that a following vehicle will not see when you are slowing down.
Fog can be patchy too, so switch the fogs on just when they are needed and switch them off as soon as it's clear again.
And remember - they are foglights - NOT driving lamps, posing lamps or fashion accessories. If you're not in thick fog or snow, leave them switched off!
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