Techno Light KTL-100 (Light emitting diode; LED), with a mounted light guide tip diameter of 4.3 mm and a blue transmission filter (225S-SPF500), were purchased from the Kenko Tokina Corporation (Tokyo, Japan). The LED output power was set to 400 mW/cm2 and wavelength to 460 nm using an optical power meter (8230E, ADC Corporation, Tokyo, Japan) before each experiment. P. gingivalis suspensions in each well were irradiated with the light source tip from the surface edge of the plate top at a depth of 10.9 mm for 96-well plates (Clear bottom black plate, Corning Incorporated, Corning, NY, USA) or 14.6 mm for 24-well plates (Clear bottom black plate, Eppendorf AG, Hamburg, Germany).