The white-light LED cluster consisting of the WW (CCT = 3183 K), red (634.1 nm), green (513.9 nm), and blue (456.2 nm) LEDs can realize the CCT tunable white-light with a CRI above 93, R9 above 90, R(9-12) above 83, and a luminous efficacies
above 70 lm/W at CCTs of 2719 K to 6497 K.
Despite the care with which the historical estimates were made, such estimates are fraught with difficulties, not the least of which are assumptions on the mix of lighting technologies used during periods when the efficiencies (or luminous efficacies) of these technologies were evolving rapidly.
In practice, the luminous efficacies of various lighting technologies are far less than this limiting value, and have evolved throughout history.
For all of the datasets, luminous efficacies were estimated directly, based on an understanding of the lighting technologies in use in a particular nation or groups of nations, and at a particular point in time.
The only exception was in the Fouquet and Pearson dataset, for which luminous efficacies were based on an evolved weighting of the proportions of old and new lighting technologies, with the underlying luminous efficacies of the various technologies based on estimates from Nordhaus' classic study (Nordhaus 1997).