(A) Trajectory of the spiral wave tip, as it drifts from the non-illuminated region to the region illuminated with LI = 0.01 mW/mm2. Colors indicate different times, here and B-C. (B) Time evolution of the voltage distribution along the dashed line indicated in (A), in a quiescent domain with the same illumination. (C) Spatial derivative of V () along the dashed line in (A), at different times, for the same illumination as in (A–B). Inset shows the time evolution of the distribution of at the interface between the illuminated and non-illuminated regions. The green curve shows the timeseries of the peak , whereas the black curve shows the corresponding timeseries for the width of the distribution in (C). We defined ’width’ as the horizontal distance between two points in the domain where . (D) Timeseries of the spiral tip speed at LI = 0.001 mW/mm2 (red) and 0.01 mW/mm2 (black). Inset shows the mean square displacement profiles corresponding to the first 800 ms of illumination, shaded gray in the speed plot. (E) Timeseries of the drift speed of the spiral core at LI = 0.001 (gray), 0.005 (light blue), 0.01 (dark blue), and 0.015 mW/mm2 (indigo). We observe that for any LI, drift speed decreases exponentially with time as the spiral core crosses the interface. (F) Slow increase in the maximum horizontal displacement (d) of the spiral core, with increase in LI applied to one half of the domain (displacement reported as mean ± SD, N = 10).