Objectives: To evaluate the bleaching efficiency of various light units utilizing bleaching agent containing titanium dioxide photocatalyst (TiO2). Methods: Labial surfaces of forty bovine incisors were ground flat, polished and stained with black tea for one week. A bleaching agent (Pyrenees, Mitsubishi Gas Chemical, Japan) contains low concentration H2O2 and TiO2 was applied on the stained labial surface followed by light irradiation for either one or five min with different light sources and intensities: (Optilux 501, Kerr, Danbury, USA; Hyper Lightel, Ushio, Gonma, Japan; G-light, GC, Tokyo, Japan; and LEDemetron 1, Kerr, Danbury, USA). In one min group the treatment was repeated fifteen times while for five min ten times. CIE L*a*b* were measured with dental chromameter (ShadeEye NCC, Shofu Inc., Japan). Data were analyzed with ANOVA followed by Tukey's HSD test and T-test (α =.05).Results: All lights induced significant change in color lightness at both times of irradiation (p<0.05), except for Hyper Lightel at 5 min because continuous activation was not applicable. Hyper Lightel showed significantly highest bleaching effect followed by LEDemetron 1 and Optilux that not different from each other in one minute activation group, however, no difference was observed in 5 min. At each application, a higher lightness was recorded in specimens irradiated for five minute than one min (p<0.05) irrespective of light source. Conclusion: The bleaching efficiency using Pyrenees was light source, intensities and irradiation time dependent.