Here are the rules from the Northern Territory - I expect that all states are the same.
Motor Vehicle Registry Information Bulletin
V14 - Additional Lighting (Driving Lights, Fog Lights)
Effective Date: 17 October 2008
Introduction
Additional lighting (such as driving lights, fog lights and search lights) may be fitted to motor vehicles in the NT providing the lights meet the requirements of this bulletin and do not compromise the vehicle’s compliance with the applicable vehicle standards.
All lighting on motor vehicles must comply with the requirements of the Australian Vehicle Standards Rules and Australian Design Rules.
Driving Lights (High Beam Lights)
All four wheeled motor vehicles must be fitted with at least two high beam headlights for the purpose of illuminating the road over a long distance ahead of the vehicle.
• Up to four additional driving lights may be fitted to the front of a vehicle - (a total of six high beam/driving lights are permitted).
• The lights must not be placed wider than the dipped or low beam headlamps and must be fitted symmetrically - (same position on both sides of the vehicle).
• The light emitted shall not cause discomfort by reflecting off any of the vehicle’s surfaces into the driver’s eyes.
• All high beam driving lights must turn off when the vehicle’s headlights are switched to low beam.
Fog Lights
Fog lights are intended to improve the illumination of the road in times of reduced visibility - which may be caused by heavy rain, smoke, dust storm or fog. These lights produce a broad flat beam. The top of the beam must not be higher than the centre of the fog light, when measured 8 metres in front of the vehicle.
Four wheeled motor vehicles may be fitted with two fog lights which must be mounted:
• symmetrically;
• no higher than the top of the low beam headlights;
• not more than 400mm from the sides (extreme outer edge) of the vehicle;
• at least 600mm apart; and
• not less than 250mm above the ground.
Fog lamps must be able to be operated independently from the headlights and driving lights. As a minimum, they must only be able to operate when the park lights are on.
The light emitted shall not cause discomfort by reflecting off any of the vehicle’s surfaces into the driver’s eyes.