An LED tube lamp comprises: an LED module for emitting light; a rectifying circuit for rectifying an external driving signal to produce a rectified signal; and a mode determination circuit for determining to perform a first mode or a second mode of lighting according to the rectified signal; wherein the mode determination circuit comprises two voltage dividers for producing a first fraction voltage and a second fraction voltage of the rectified signal, and a control circuit coupled to the two voltage dividers and configured for receiving the first fraction voltage and for receiving the second fraction voltage. When the first fraction voltage signal is in a first voltage range, the mode determination circuit determines to perform the first mode of lighting; and when the second fraction voltage is in a second voltage range, the mode determination circuit determines to perform the second mode of lighting.