The Visual Fault Locator (VFL) Pen has a visible red light source centered on 650nm. The RPEN-210 is a necessity tool that should not be missing from any fiber plant manager or fiber optic installing technician. VFLs typically use a 650nm wavelength red laser that is transmitted through the fiber. Tool sends visible light over a fiber strand with a 10mW power, good enough to reach. Luxbond LBTEK Fiber Optic Red Light Pen (also known as a pen-style visual fault locator or fiber optic fault detector) uses a 650 nm semiconductor laser as the light source.