||This Wheat Special Report analyzes the effects of radiation and temperature on the date of flowering and grain yield of spring bread wheat cropped under optimum conditions. The experiments were conducted at Ludhiana, Punjab, India, over 7 years and using a range of genotypes. The optimum flowering date for maximization of wheat grain yields is confirmed to be when the ratio of radiation to temperature (PTQ) is at its maximum. The individual effects of radiation and temperature on yield and yield components at various stages of crop development are also examined. We hope that the concepts validated here will be useful elements of wheat component agronomy in the development of new spring wheat varieties and better agronomic practices for wheat grown under irrigation (Mega-environment 1). This short version (No. 23a) does not include the raw data that may be of interest to some scientists. This information (Le., correlation coefficients for the three genotypes used in the experiments, means averaged across reps, and climatic data) is provided in Appendices 2 through 5, which are included in No. 23b. S.S. Dhillon is an agronomist with the Department of Plant Breeding, Punjab Agricultural University, Ludhiana, India, and J.1. Ortiz-Monasterio R. is an agronomist, with the Wheat Program, Crop Management and Physiology Subprogram, CIMMYT, Mexico.