In this study, we performed optical simulations for two light sources: internal and external electrode light sources. Based on the optical simulation results, we created a practical design to verify the design validity and extract optimal design factors for each light source. The three key geometric variables in the design of a direct-lit flat panel light source are the distance between the two lamps, the distance between the lamps and the reflector, and the number of lamps. These variables significantly impact the optical design and determine various characteristics of the flat panel light source system. In this study, we used a 26 mm distance between the two lamps, a 4.5 mm distance between the lamps and the reflector, and a total of 20 lamps to derive optimal values for these variables. Under these conditions, we created a practical design and evaluated its performance, achieving an excellent flat panel light source with a central luminance of 6,423 nits and a luminance uniformity of less than 5%. This study demonstrates that optical simulation techniques are an effective method for designing a surface-emitting light source system for medical LCDs, demonstrating the feasibility of achieving high performance while maintaining a low cost.