Motor Vehicle 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.
This is one area where you must read statutes and regulations together in order to find the answer to your questions.
New Hampshire statutes and regulations use the words "lamps" and "lights" interchangeably. (Perhaps the word “lamp” harkens back to the days of horseless carriages?) Because of this, the print index to the statutes may be more helpful than keyword searching online. Look under the term “motor vehicles” and then for the subdivision “Lights and Lighting.” Once you get to the appropriate RSA chapter, look at the beginning of the chapter which gives a list of subdivisions and shows you the context of all of the statutes in that section.
(Don O'Brien [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons)