Lum's guide to proper fog light use

artbaron

Mrs_Imp wrote: »

Sometimes it's unavoidable. I did the Snake Pass one winter's night. Halfway over, we hit thick fog. It wasn't safe or practical to stop. I ended up driving at walking pace with DH looking out of the side window watching the edge of the road, I kept a close eye on the centre white line, while watching for oncoming cars.

I had that on Corney Fell in Cumbria many years ago, it was unbelievable, like the fog you get in old fashioned horror movies. We literally couldn't see the road at all, not even a glimpse, so the passenger had to get out and walk along side the car just in front of the nearside headlamp, banging on the bonnet and making arm gestures as a guide.

neilmcl

photome wrote: »

Does it matter if the car in front disappears, so long as you are driving to the conditions

No, but you would want your own vehicle seen by anyone coming from behind, hence the use of rear fogs in reduced visibility.

jaydeeuk1

Came back on m1 from sheffield about 5.00, foggy but visibility about 500 metres. Huge number of morons with fog lights on and sticking to the middle lane probably because they 'felt safer' need slapping. Amazing the number of people who forget how to drive when it gets foggy, or rainy, or sunny.

If you were driving a white VW polo reg FE58 X.. then please hand your licence back, it was dark, and yes people were flashing you to remind you to turn some lights on, not let you pull out.

Wig

Mrs_Imp wrote: »

I do use fogs in heavy spray on the motorway if I find the cars in front of me disappearing.

Yes, ok, but you do realise that 100m visibility is approximately the distance between 2 slip road 100yrd marker signs, so you would have to be in a real shitstorm, not to be able to see the car infront within 100 meters. It doesn't happen very often in my experience. 25 years driving maybe I've used my fogs 4 times in Fog and once in rain.


On a side note I was wondering the other day how to put a really mega bulb into my rear fogs so that when that Charlie behind me has his beams on full or he has xenons dipped but seriously out of alignment ... I can burn that sucker's retinas out. Not very PC of me of course, but they annoy the crap outta me.

On another side note as the visibility is supposed to be 100m or less for fog lights... What does that do to your stopping distance, i.e. there must be a calculation to make to show that at 60mph your stopping distance is going to be X and if you can't see further than 100m than means if you are using fogs (properly) at 60 mph you are going to kill yourself.... so there must be an appropriate speed to use if you use your fog lights....What is it?

Wig

Mrs_Imp wrote: »

As others have rightly pointed out, fog lights should be used in conditions of reduced visibility. If I'm dazzling you with my rear fog light, it's time to back off, because you're too close.

No, Fog lights should only be used in conditions of SERIOUSLY reduced visibility..... 100m or less.

Joe_Horner

Wig wrote: »

On another side note as the visibility is supposed to be 100m or less for fog lights... What does that do to your stopping distance, i.e. there must be a calculation to make to show that at 60mph your stopping distance is going to be X and if you can't see further than 100m than means if you are using fogs (properly) at 60 mph you are going to kill yourself.... so there must be an appropriate speed to use if you use your fog lights....What is it?

Ignoring "thinking distance" for simplicity:

where:
V = change in velocity (in m / s)
D = distance travelled (in m)
A = acceleration (in m / second squared)

D = (V squared) / A
V squared = DA

Assuming reasonable brakes in reasonable conditions, A will be about 6.4 m / second squared so, with D = 100m:

V squared = 640
V = 25.3 m/s
= 90km/h

Which is about 56 MPH

If your brakes are good and the road's good (unlikely in conditions where fogs are needed) you might get about 8.5 m / second squared for A, which would let you stop in 100m from 29 m/s or about 65 MPH

If the road's bad (grease / water / snow / dead locusts) it's more likely to be around 50MPH physical stopping distance.

Mrs_Imp

Wig wrote: »

Yes, ok, but you do realise that 100m visibility is approximately the distance between 2 slip road 100yrd marker signs, so you would have to be in a real shitstorm, not to be able to see the car infront within 100 meters. It doesn't happen very often in my experience. 25 years driving maybe I've used my fogs 4 times in Fog and once in rain.

Yep. I ended up pulling over on to the hard shoulder as it was so bad that it was too dangerous for me to drive any further. When it eased a bit I carried on going, then drove through the River Avon, which was across the road :eek: A short while later my car stopped after a lorry splashed through the next flood and got water in my points. I spent 6 hours in my car (4 hours of which the motorway was closed) before a police landrover rescued me, and 24 hours in the services before Mr Imp could get through the floods to rescue me. My car was recovered 3 days later.

On a side note I was wondering the other day how to put a really mega bulb into my rear fogs so that when that Charlie behind me has his beams on full or he has xenons dipped but seriously out of alignment ... I can burn that sucker's retinas out. Not very PC of me of course, but they annoy the crap outta me.

You and me both!!

Mrs_Imp

Wig wrote: »

No, Fog lights should only be used in conditions of SERIOUSLY reduced visibility..... 100m or less.

Tsk. Nitpicker Sorry, I missed out a word. I somehow assumed that people would understand that I meant <100m visibility, as that had come up in other posts.