Information taken from lux review.
If your workspace is still lit using 4 x 18W recessed fluorescent units, you really ought to change them. There is a huge range of more efficient LED ceiling panels available. We have tested 10 panels from the cheapest and most cheerful to quality engineered units with sophisticated optics. We could easily have tested 10 more. We have tested both the thin flat panel (edge-lit) types and the deeper troffer types, which are backlit.