The Y3Handheld Optical Power Meter & Red Light Pen All-in-One Series is a professional tool designed for continuous optical signal power measurement and fiber continuity testing. Controlled by a high-performance microprocessor, it ensures accurate and efficient fiber-optic. Check each product page for other buying options. Find portable testers for network installation and maintenance work. VFLs typically use a 650nm wavelength red laser that is transmitted through the fiber.