The method of chemically induced dynamic nuclear polarization in a switched external magnetic field (SEMF CIDNP) is applied here for the first time to an experimental study of short-lived neutral radicals in homogeneous solutions. With three photochemical reactions it is exemplified, that SEMF CIDNP allows investigations of the kinetics of the transient species with high time-resolution as well as a determination of their spin relaxation times in low magnetic fields. A theoretical approach is developed, which permits simulation and analysis of the experimental data. In weak magnetic fields (0.5-2.0 mT) the effective spin-lattice relaxation times for the decay of the chemically induced spin polarizations in benzyl, tert-butyl, and 2-hydroxy-2-propyl radicals are found to be T-1=(3.8+/-0.5) mus, T-1=(7.8+/-0.5) mus, and T-1=(2.5+/-0.5) mus, respectively, in benzene solution at room temperature. They are in fair agreement with relaxation times determined by time-resolved X-band electron paramagnetic resonance spectroscopy at strong magnetic fields (approximate to350 mT).