Shalu, I thought some more on these calculations, and I realized that when calculating the efficiency we should use the proportion that the wattage increased, not the 1x, 2x, 3x, 4x because the power did not increase in practice or in reality by double, triple, quadruple, as we attempt to do by overdriving the lights. We know this thanks to your use of the Kill-A-Watt. So, for the T8 bulb at 4x overdrive, the OD Efficienies calculation would look like 4.6/(3.8*(69/40))=.70 or 70% efficiency. So, as 100% efficiency for 1x as the basis, for all the T8 OD Efficiencies, I calculated 2x = 85%, 3x=78%, 4x=70%. These figures are in agreement with estimates elsewhere on the web.