Same with me... not so much the "F" code but in thinking it a simple concept. Nope, not so much. Really good and free on-line PDF type book that's recognized by experts as a source to read comes from Osram/Sylvania. Go to the Sylvania website, do a search for say a EVC lamp, than scroll down and look for their further readings and texts. Pull up something like their low voltlage lamp technology PDF. Print it up an read it over a few days. This text while written in a language all can understand is a sort of bible for all one needs or wants to understand about lamps. Further info is their PDF's about arc lamps but read this and you will understand most questions. After that, it's ANSI code, Lif code and J-Code, what make them up and how to understand them. Read the Osram text and the follow up question this in ANSI code is simple, it's an American National Standards Institute guideline for all lamps of this specific class which no matter the brand fit within a certain broad guideline. Same with the Lif Code lamps and J-Code lamps per definition though more broad. Understand what the lamp spec is and how it changes and you understand how the ANSI code workssssss - this for voltage/wattage/amperage of the lamps also. Granted you tend to want to understand voltage/amperage/wattage as definitions also. Some lamps flow voltage or sealed beam lamps or instance don't list wattage, they list amperage. Such a question thus is sensible, but still an understanding of it all is important & makes amperage verses wattage a non-question.After following all of the advice above also take a minute to understand the bewildering fact that there is no "magic code" to ANSI classification of lamps. By that I mean, an FEL, and an FHG have almost nothing in common. When I first started out I thought , "Oh, the F means something and the E means something, and the L means something...." Nope just random letters assigned to random lamps. I love Technocrats.