1. A voltage detection circuit, comprising:an impedance coupled between inputs of an LED tube;
a voltage detector configured to detect a voltage across the impedance;
a voltage threshold circuit configured to provide a threshold voltage;
a first control circuit configured to compare an input voltage across the inputs of the tube to the threshold voltage, and to control the voltage detector to detect the voltage across the impedance when the input voltage is less than the threshold voltage; and
a second control circuit configured to enable the voltage detector when the voltage threshold circuit is charged to a starting voltage;
wherein the voltage threshold circuit comprises a first capacitor and the detection circuit comprises,
a first charging loop configured to charge the first capacitor to reach the starting voltage; and
the first control circuit further comprises a transistor adapted to connect the impedance between the input voltage and a power ground, and the transistor is adapted to be turned on to begin the detection and is adapted to be turned off when not detection.