Everything you're about to read is based on one, single, simple principle and that is that...
Your lights are there primarily to help other road users to see you first and foremost, and NOT to light the road ahead of you to allow you to see where you're going in the dark
You have several sets of lights on your car...
- Dipped beam head lights and tail lights - the usual lights you'd use if it was dark
- Side lights - for use when parked in dark areas or where a speed limit greater than 40mph is in force (how many knew that was a legal requirement eh?)
- Main beam head lights - for use where it is very dark and there are no other road users in sight
- Fog lights - for use whenever visibility is less than 100mtrs (usually in fog, but not restricted to that - I'd advise using them in extreme snowfall too, but never in rain)
- Indicators - for communicating an intention to turn left and right of course
- DLR (Daylight Running Lamps) - regularly confused with "headlights are always on", these are brighter versions of front sidelights which help others to see you as you approach them in good weather conditions. They don't work at the rear of the car to avoid any confusion with brake lights
- Hazard lights - to be used when the car is causing a temporary obstruction in the road or when approaching standstill traffic on either a motorway or a national speed limited dual carriageway
And this is when we'd usually advise people learning to drive to use them....
Fantastic weather - a good, clear day with great light levels, no chance of rain and dusk is several hours away yet
These are the conditions that DLR's were designed for - all new cars sold since 2010 have them fitted and drivers of older cars should consider using dipped beam headlights to reduce their road risk
Overcast and cloudy - it might rain or go dark in the next 90 minutes
Dipped beam headlights should be on in these conditions and may need to be selected manually on those cars with automatic headlights
Raining - regardless of how heavy it is
Dipped beam headlights - some cars with automatic headlights will turn the dipped beams on when the wipers are in use, but for the avoidance of doubt, turn them on manually
Any other "bad weather" including mist, fog or snow
Dipped beam headlights - turn them on manually to avoid getting caught out
Broken down
Side lights are ideal for this in addition to the hazard lights of course. It isn't a legal use of the fog lights, but I recently read one article that suggested that using them in a breakdown situation might help to make you more visible to other drivers and reduce your risk of having the vehicle struck by another one whilst you wait for a pickup. Use your own judgement on this idea.
You'll notice that side lights are never used when driving. This is because they are dimmer than the DLR's that will often turn off when side lights are selected manually - they are parking lights and effectively useless at making you more visible to others.
You will also notice that I don't reference the legal requirement from the Highway Code that says that "dipped beam headlights MUST be used when visibility is less than 100mtrs". My reasoning for this, is that this legal specification is totally inadequate in the pursuit of reducing road risk. It effectively means that you are not breaking any laws if you drive around in fog with no lights on at all as long as the visibility is more than 100mtrs, which is absolute madness (especially if your car is dirty, or silver in colour).
Stay safe everyone!