Nowadays, usage of artificial light as the supplemental light in greenhouse cultivations is one of the most common techniques to increase greenhouse productions. Greenhouse is part of the Smart Grid, where the activation of electricity energy market is applied. With Real-Time Pricing (RTP) of electricity energy, finding the optimum values of supplemental light for various cultivations and conditions in the greenhouse environments is very important. In this paper, by modeling and using the measured and presented data of cherry tomato in the greenhouse cultivation, the optimum amounts of supplemental light and required electrical energy for HPS lamps in the greenhouse environment are simulated and calculated.