When a signal is present, the blue LED will light. Note: It will take several minutes for the LED to turn from blue to red after the input signal to the subwoofer is removed. Due to JBL's unique high-output, high-efficiency amplifier design, power consumption is minimal when the subwoofer is not receiving a signal. Of course, the subwoofer can be turned off with the main power switch, whenever desired, if you do not wish to leave it in auto (standby) mode. Use of the main power switch is recommended for vacations, etc. · Specification correction (to early copies only): In the specifications, under section Low-Pass Crossover Frequencies, if there is a 2nd part stating "150Hz when using speaker-level connection " that statement should not be there. It should be included in the section Outputs, as this is a reference to a 150Hz Hi-Pass filter for the satellites, only noticeable when using the speaker level connection. · Use of a Y-cable Section - Speaker Connections, if using DOLBY PRO LOGIC (NON-DIGITAL) ­ LINE LEVEL: In the right-hand column in this section it says a Y-cable is not included. That is incorrect; a Y-cable was supplied with this product. But the included Y-cable will not work exactly as the manual instructs; the o/m describes the use of a one male-to-two female connector. The supplied Y cable is a one female to two-male connector. This cable will also work, but the connection should have been described this way: "Plug both male ends of the Y-connector into the L8400P's line-level IN jacks. Then plug in a single separate RCA type interconnect cable (not supplied) into the Y cable. Finally, plug the other end of the single cable into your receiver's subwoofer jack...