What do the LED lights on Lt Sensors indicate?

The Lt Sensors perform a diagnostic self-test each time they are plugged into a USB port. The status of the sensors is indicated by the appearance of the LED light on the lead-end of the biopotential sensor, or the USB-end of all other sensors. 

When you connect it to your computer for the first time, you should test that the sensors are functioning properly, as follows: 
Connect the Lt Sensor to a USB port. Ensure that the computer (or USB hub) is turned on.
Observe the LED light indicators in the sensors as they connect. The table below describes the various states of connection associated with the appearance of the LED light.

Status Indicator  Meaning
No light.        If the indicator light does not light up, then there is a problem with the power source or power cable. Check the connections and cables.
Green         The sensor is idle, initialized, and waiting for a command from the computer. 
Blue The sensor has been detected by Lt.
Light Blue The sensor is sampling.
Orange flashing The sensor firmware is being updated. Unplugging the sensor during this time will interrupt the update process. Leave the sensor plugged into the USB port until the status light turns green or blue. 
Red flashing The sensor is in an error state.