I only know what I've read, This except from NZTA seems pretty clear but like everything I guess it's open to interpretation and therefore inconsistent across vehicle testers. Dipped beam headlamps Dipped beam headlamps are used for lighting the way ahead of the vehicle at night. The beam pattern is controlled so that the driver can see the road ahead without causing glare to other road users. (Dipped beam and main beam headlamps are often combined into one lamp.) Fitting requirements All vehicles are fitted with one or two dipped beam headlamps as original equipment. You may not fit any additional dipped beam headlamps to a vehicle. Dipped beam headlamps must be white or amber in colour. On the road Dipped beam headlamps should be used during the hours of darkness and whenever visibility is poor. Because they are dipped, they can be safely used in all conditions without dazzling other road users. Main beam headlamps Main beam headlamps are used for lighting the way a long way ahead of the vehicle. Because they are not dipped, they will dazzle other road users if not used properly. (Dipped beam and main beam headlamps are often combined into one lamp.) Additional main beam headlamps are also known as ‘driving lamps’. Fitting requirements (original equipment) Most motorcycles, cars and trucks are fitted with one or two main beam headlamps as original equipment. Main beam headlamps must be white or amber in colour. Fitting requirements (additional equipment) You may fit additional main beam headlamps (driving lamps) as long as you don’t have more than the maximum allowed for that type of vehicle. All vehicles except motorcycles may have up to four main beam headlamps (motorcycles may have up to two). For example, if your car has two main beam headlamps you may add two more, but if it already has four main beam headlamps you may not fit any more. Main beam headlamps must be wired so that they automatically switch off when the headlamps are dipped.