Human adipose-derived stem cells (hASCs) have the potential to differentiate into several different cell types including osteoblasts. Photobiomodulation (PBM) or low level laser therapy (LLLT) using red or near-infrared wavelengths has been reported to have effects on both proliferation and osteogenic differentiation of stem cells. We examined the effects of delivering four different wavelengths (420?nm, 540?nm, 660?nm, 810?nm) at the same dose (3?J/cm(2)) five times (every two days) on hASCs cultured in osteogenic medium over three weeks. We measured expression of the following transcription factors by

RT-PCR:

RUNX2, osterix, and the osteoblast protein, osteocalcin. The 420?nm and 540?nm wavelengths were more effective in stimulating osteoblast differentiation compared to 660?nm and 810?nm. Intracellular calcium was higher after 420?nm and 540?nm, and could be inhibited by capsazepine and SKF96365, which also inhibited osteogenic differentiation. We hypothesize that activation of light-gated calcium ion channels byblue and green light could explain our results.