Temporal emission characteristics of two kinds of white light-emitting diodes (LEDs), NSPW300BS (Nichia Co.) and E1S09-OW1AP-02 (Toyoda Gousei Co.), for high-speed repetitive pulsed current have been studied. The structure of the two LEDs are slightly different: The former utilizes fluorescence from YAG materials excited by a blue LED together with the blue LED light itself, white the latter utilizes that from some kinds of composite materials excited by an ultraviolet LED. Each LED was driven by a laboratory-made, nanosecond, high-current, pulse generator using an avalanche transistor. As was expected, the fluorescence decay times for the two LEDs were fairly different. The fluorescence decay time of the Nichia's LED was about 75.0 ns, while that of the Toyoda's LED was ranging from a several hundred nanoseconds to a few milliseconds depending on the emission wavelength. Introducing a time-resolved light-detection technique, the pulse-driven white LED appears useful for some kinds of sensor applications as a wavelength-variable light source.