1 r 2 gt vth 2 gt u2212 vs 1 u2212 vf assume the node voltage on the source electrode of the first switch q 1 is va the node voltage on the source electrode of the second switch q 2 is vb and the node voltage on the gate electrodes of the first switch q 1 and the second switch q 2 is vc the control method of the led module l according to this embodiment is described as follows when the primary led 1 is normally working va vs 1 u2212 vf vc vs 1 u2212 vf r 2 r 1 r 2 a voltage difference between the gate electrode and source electrode of the first switch q 1 is vgs 1 vc u2212 va therefore vgs 1 u2212 vs 1 u2212 vf r 1 r 1 r 2 since vth 1 gt u2212 vs 1 u2212 vf r 1 r 1 r 2 therefore vgs 1 lt vth 1 which satisfies a switched on condition for the first switch q 1 the first switch q 1 is then switched on in the meantime assume the spare led 2 is also switched on then vb vs 1 u2212 vf and the voltage difference between the gate electrode and source electrode of the second switch q 2 is vgs 2 vc u2212 vb therefore vgs.