Answer: 1. the use of 1P lighting, traditional practice, nothing is not bad. It also has 1P+N, and I don't think it's necessary. There is no leakage of electricity in the lighting.

2. actually use 1P+N, like DPN switch, and 1P switch modulus!

3. lighting in general use 1P, residential standards mentioned residential bathroom lighting should be with leakage protection, so the bathroom lighting circuit can be 1P+N with leakage protection. However, we do not mention that we use 1P in general lighting.