113
You MUST

• ensure all sidelights and rear registration plate lights are lit between sunset and sunrise
• use headlights at night, except on a road which has lit street lighting. These roads are generally restricted to a speed limit of 30 mph (48 km/h), or 20mph (32km/h) in Wales, unless otherwise specified
• use headlights when visibility is seriously reduced (see Rule 226).

Night (the hours of darkness) is defined as the period between half an hour after sunset and half an hour before sunrise).
Laws RVLR regs 3, 24, & 25, (In Scotland - RTRA 1984 sect 82 (as amended by NRSWA, para 59 of sched 8))

114
You MUST NOT

• use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists and horse riders
• use front or rear fog lights unless visibility is seriously reduced. You MUST switch them off when visibility improves to avoid dazzling other road users (see Rule 226).

In stationary queues of traffic, drivers should apply the parking brake and, once the following traffic has stopped, take their foot off the footbrake to deactivate the vehicle brake lights. This will minimise glare to road users behind until the traffic moves again.
Law RVLR reg 27

115
You should also

• use dipped headlights, or dim-dip if fitted, at night in built-up areas and in dull daytime weather, to ensure that you can be seen
• keep your headlights dipped when overtaking until you are level with the other vehicle and then change to main beam if necessary, unless this would dazzle oncoming road users
• slow down, and if necessary stop, if you are dazzled by oncoming headlights

116
Hazard warning lights. These may be used when your vehicle is stationary, to warn that it is temporarily obstructing traffic. Never use them as an excuse for dangerous or illegal parking. You MUST NOT use hazard warning lights while driving or being towed unless you are on a motorway or unrestricted dual carriageway and you need to warn drivers behind you of a hazard or obstruction ahead. Only use them for long enough to ensure that your warning has been observed.
Law RVLR reg 27