Low-power lasers (LPL) in the visible have already been shown to exert bioeffects on various cell cultures. In this work we show that photobiostimulation can also be induced by a non-laser device emitting a broad-band in the visible range (400-800 nm), and that this light-cell interaction is probably mediated by hydrogen peroxide formation. A single exposure of fibroblasts to broad-band visible light resulted in their enhanced proliferation with a maximum at 5J/cm², similar to our previous results where the light source was a HeNe laser. The presence of superoxide dismutase (SOD) or catalase (CAT) in the culture medium during irradiation or immediately afterirradiation suppressed this enhanced proliferation. An enhanced cell proliferation was also achieved when the cells were incubated with H₂O₂; or SOD for 30 min without irradiation. The fact that light mimics chemostimulation by H₂O₂ leads us to believe that light-tissue interaction involves H₂O₂ formation. As more direct proof, we measured the chemiluminescence (CL) of irradiated cells, and the increase that we found in CL indicates H₂O₂ formation.