This research investigate the role of light flashes as environmental stimuli during different incubation periods in improving the embryonic development and hatch performance of Rhode Island Red chicken eggs. A total number of 900 hatching eggs were incubated using 1 of 5 light flashes regimens as follows: The first group (control, C) was incubated under dark conditions throughout the whole incubation period. While, the second group (T1) was incubated using light flashes conditions during the 1st week of incubation period. The third group (T2) was incubated using light flashes conditions during the 2nd week of incubation period. The fourth group (T3) was incubated using light flashes conditions during the 3rd week of incubation period. The fifth group (T4) was incubated using light flashes conditions throughout the whole incubation period. Results indicated that incubated light flashes treatments (T3 and T4) had significantly better embryonic development, hatchability and chick weight or relative weight gain than darkness conditions. Percentages of late dead embryo and incubation period (hrs) were significantly lower when egg exposed to light flashes during the 3rd week of incubation compared to others groups. Also, light flashes significantly increased chick breast, liver, ovary and residual yolk sac weight at the 2nd day of age. However, insignificant differences of body temperature, embryonic lengths, embryonic chemical composition, embryonic mortality (early and middle), piped eggs, malpositioned embryos, egg weight loss, yolk-free body mass, chick sex, culled and chick weight loss and quality scores were observed among all experimental groups.