Like in all fields related to the design and construction of buildings, the lighting design process implies the use of standards, as it is typically required to demonstrate the compliance with nationally and/or internationally established standards for different types of functions and situations. In this context, the codes and standards can be seen as tools, and examined in view of their effectiveness in supporting the lighting design process. This paper will focus on two dimensions of the usability of lighting standards - the basic level of usability, tested through experiments on students having to tackle basic tasks while handling the standards for the first time, and a more advanced level, revealing problems of usability of the standards content itself inside the practice, by talking with lighting professionals and investigating the problems they found in their years long experience of working with standards. The contribution of this paper is firstly a framework of possible methods of investigating the usability of regulating documents such as standards and other guidelines, and then the results of the analysis, pointing to the identified problems and suggestions for the improvement of the usability of lighting standards. Most suggestions will however apply to all other kinds of building design standards.