Reproducible properties of a large number of GaP p-n junctions made by either in-diffusion or out-diffusion of Zn were studied with emphasis on room temperature measurements. The I-V characteristics are due to space-charge recombination and are accounted for in detail by the Sah-Noyce-Shockley theory. The dominant forward-bias electroluminescence (EL) in out-diffused diodes is proven to be Zn-O acceptor-donor pair recombination at both 77 (hν=1.82 eV) and 298°K (hν=1.78 eV) from its spectral position and the shift of this position with substitution of Cd for Zn. The nonexponential time decay of this red EL in out-diffused and in-diffused diodes at 77°K also establishes it as a pair recombination mechanism. The red EL in the latter diodes at 298°K shifts anomalously in spectral position with current, thus preventing a firm identification of its mechanism at 298°K. Measurements of the spatial distribution of the red EL in all diodes show it to be generated principally in the carrier-diffusion region on the p side of the junction in a layer which saturates in brightness and then expands in width. Green EL is generated in or very near the space-charge region. By a novel use of the green EL to measure the junction bias the red EL and the I-V characteristics are studied to very high junction biases. The red EL is found to vary as exp(qVmkT) where m=1, 2, and ~1 in successive regions. These facts, the spatial distributions, and the transition voltage between the first two regions, are in good agreement with the predictions of the preceding paper. It is shown that at the highest junction biases (~2.0 V) n-side injection dominates the I-V characteristic and causes a decrease in the red EL quantum efficiency. External quantum efficiencies at the optimum bias (~1.8 V) as high as 7×10-3 are found at 298°K. Several characteristics of the green and infrared EL are also given.