For decades, the straight-tube fluorescent lamp has been top in efficiency and ubiquitous in indoor lighting. Justifiably, the "four-footer" is one of the last lighting types to be displaced in the LED Revolution. But under what circumstances is replacement warranted, and with what? Many are blithely retrofitting one-for-one with LED tubes and kits, achieving dramatic energy cuts, but with insufficient regard for technical, lighting, and safety considerations. Meanwhile, the line between retrofit and new-construction is blurring: code now requires that if 50% of lighting is replaced, then the space must meet strict W/sf and controls requirements. New LED fixtures can now exceed fluorescent in energy efficiency in numerous applications. The best of smart, energy-sophisticated LED lighting, offers responsible, deep savings, and can become much more the norm. With the advanced LED Revolution comes the need for more technical know-how.