a) Field of view (FOV) of active region AR 11520 observed in the AIA 211 Å channel on 11 July 2012. The active region is relatively clear of coronal loops and other complex coronal structures, therefore, the light bridge is easily identifiable. Smaller FOV (as enclosed in the dashed rectangle in a)) observed in the AIA b) 211 Å (2 000 000 K), c)171 Å (600 000 K), and d) 1600 Å (5000 K) channels, respectively. The green crosses label the pixel where time series were extracted and analysed in Fig. 2. The dot-dashed rectangle in b) indicates the area where power maps are calculated and analysed in Fig. 3. e)−g) Evolution of the local normal magnetic field measured by Hinode SOT/SP on 11, 13, and 14 July 2012, respectively. The contours in d) and e) show the light bridge structure at upper photosphere (1600 Å) as a reference.