Electric fields on the ground 500 m, 5 km, and 50 km from the lightning channel base computed using the transmission line (TL) and antenna theory (AT) return-stroke models for a typical subsequent stroke current at the channel base and a return-stroke speed equal to the speed of light (v = c) are compared. The AT model gives a total electric field peak that is about 10% lower than the field peak predicted by the TL model. Optical measurements of the return-stroke speed within the bottom 100 m of the lightning channel are reviewed and found to be not supporting the assumption of v = c.