Background: Photobiomodulation therapy (PBMT) devices for hair loss have been popular for many years. But most treatment modules are decided empirically, and no objectively accepted parameters have been proposed. We attempted to identify the optimal PBMT parameters for hair growth. Methods: A dome-shaped laser diode (LD)/light emitting diode (LED) module was applied to C57BL/6 mice. Each device had different LD modules in terms of numbers, total energy, and treatment times. Negative control and 3% minoxidil positive control were co-investigated. The 3 mW LDs with 5, 10, and 15 mm spacing were applied 3 or 5 times a week. Results: The dome-shaped LD/LED modules effectively induced earlier telogen to anagen transitions and increased hair follicle density. The effect was greater with decreasing spacing and increasing dose and treatment numbers. Immunohistochemistry analysis showed an increased β-catenin/Sonic Hedgehog expression similar to minoxidil, and an increased proliferation rate of fibroblast growth factor-7 (keratinocyte growth factor). Conclusion: Increasing LD/LED module numbers, power, and treatment numbers may increase the effect of PBMT on hair regrowth.