Hi Simon, unfortunately there is a bewildering amount of information to absorb to find that out. If you look into the tech. literature you will find that twin fluorescent give out circa 7000 lumens the only equivalent I have come across is KSR twin LED battens. They are really bright (7000 lumens). The way lumens are measured seems to bear no relation to the real life radiance received on the critical areas as the way lumens are measured by different manufacturers vary. Stated lumens may have no bearing on the lumens delivered to the desk say. Having said that, the human eye is very adaptable and incapable of assaying how much light there is except at very high levels. So if you put in the KSR ones the amount of fittings you will need will be less. As the fittings they put fluors. in block 60% of the light from the tube whereas LED radiate all around so to speak so perceived levels of lighting will be experienced as far brighter. So if you have 8 fluors to replace you may only need four LED. Also there are requirements for lumens delivered at desk height and need to be measured to comply. In short it is best to ask the manufacturer and tell them for what purpose and get in writing from them what is needed to comply with these requirements, sorry to take so long to say that.