jfanning: In saying that the law doesn't say what the maximum brightness of a light can be.
Well not directly but you still cannot purchase bulbs that are more powerful then specified for the car as below.
Replacement bulbs
- If you want to improve the performance of your headlamps, you can replace the bulbs with high-efficiency bulbs. However, these replacement bulbs must be of a similar type and wattage as the original bulbs, eg don’t replace a standard bulb with one of higher wattage.
So although you can get lights that are brighter they must not be a higher wattage, they also are restricted in how blue they are. In fact for cars imported from Japan you may be forced to go with lower wattage as some come with high wattage dipped beams that you cannot legally buy in NZ.
Quote is from http://www.nzta.govt.nz/resources/get-your-lights-right/get-your-lights-right.html