There are four individual LEDs on the Tellurium.
Two are located in the area which contains the on-board 3.3V and 5V power supplies. When lit, these indicate that the associated supply is powered (the silkscreen text adjacent to each LED indicates which LED is associated with which supply).
There is an orange LED which is located adjacent to the USB hub IC (device marked NXP ISP1520). When the USB hub is operational (hence a host linked with the Colibri USB port is present) this LED will pulse at the rate of approximately 1Hz. During normal operation, this LED should be pulsing. Any other state indicates the hub is not functioning correctly.
The fourth LED is a green LED located in the vicinity of the USB client port (mini-B connector). This LED will light to indicate when a connected USB host device is providing power to the port.