Optical receivers often drive a “LOS” (Loss Of Signal) indicator, where lit or blinking LOS lights flag a missing or weak optical input. Meanwhile, a separate link LED shows whether the module has locked to the light level and negotiated. They tell you several things about the network connection. For enterprise IT teams and engineers using Router-switch devices, these LEDs are often the first indicator of network health. When you know how to read status LEDs, you can confirm connections at a glance, spot speed mismatches before they slow you down, and zero in on a bad. System activity and status can be determined through the activity of the LEDs on the switch.