This guide got started because a caller to the Law Library asked why she couldn't have headlights of a certain color on her car. That led us to look at all sorts of other issues regarding automobile lights.
As is common, federal law in this area sets the minimum standards for motor vehicle safety. States may set higher standards if they wish but they must at least meet the federal standards. Also, this is one area where you must read statutes and regulations together in order to find the answer to your questions.
There are liability issues that may arise if lights are absent or insufficient. The two articles below discuss some of those issues.
Although this Wikipedia entry does not focus on New Hampshire law, it does provide background information, giving an interesting and detailed discussion of many aspects of automotive lighting from an international perspective. Topics discussed include history, color of lighting, forward illumination, conspicuity, signal and identification lights (front, lateral, rear, large vehicles, emergency vehicles, retroreflectors, experimental systems and research and development), convenience lights, on service vehicles, many footnote references, many photos, and external links.