Directional lamps are commonly specified based on their luminous intensity distribution. Figure 1 illustrates the relationship between three descriptors of distribution: center beam candlepower (CBCP), beam angle, and field angle. Complete descriptions of these terms, among others, are included in Appendix A. Of these, beam angle is the most widely cited value in manufacturer literature and on product packaging. ANSI recommends the following system for identifying the nominal beam angle of PAR lamps: