The EXFO ELS-500 is an Optical Light Source provides excellent stability and high measurement accuracy with your choice of two wavelengths (850/1300 nm or 1310/1550 nm) on a single port, or four wavelengths (850/1300 nm and (1310/1550 nm) on two ports. With its automatic wavelength switching mode, it is the perfect complement to the EPM-500 Power Meter when it comes to quickly and easily measuring attenuation on fiber-optic links. The ELS-500 features tone generation for use with the EPM-500 Power Meter, automatic wavelength switching, and the highest singlemode output power in the industry.