Commands used in DALI are described as ARC Power Control. If I am Directing an LED fitting to a particular dimming level, what about the command has any relevance to an 'ARC' description. Where does 'ARC' fit with the DALI protocol for Dimming a fitting? New User ... Very impressed your resource... Thank you for it.
This term is a hangover from the original standard which was for fluorescent lamps only where it was used to differentiate between the power in the lamp and the power drawn from the supply by the ballast.
DALI started off as an annex to IEC60929 "A.C. supplied electronic ballasts for tubular fluorescent lamps - Performance Requirements" Annex E.4 - Control by Digital Signals. It is now IEC62386.
Subsequently, the standard has added support for many lamp types which do not use arcs to generate light, including low voltage halogen, incandescent and LED, but the term has remained for historical reasons.
Within IEC standards, terms not given in the definitions section should be found in Electropedia.