Jamieson, Fausset and Brown on Isaiah 50:11

11. In contrast to the godly (Is 50:10), the wicked, in times of darkness, instead of trusting in God, trust in themselves (kindle a light for themselves to walk by) (Ec 11:9). The image is continued from Is 50:10, "darkness"; human devices for salvation (Pr 19:21; 16:9, 25) are like the spark that goes out in an instant in darkness (compare Job 18:6; 21:17, with Psa 18:28).

sparks--not a steady light, but blazing sparks extinguished in a moment.

walk--not a command, but implying that as surely as they would do so, they should lie down in sorrow (Jr 3:25). In exact proportion to mystic Babylon's previous "glorifying" of herself shall be her sorrow (Mt 25:30; 8:12; Re 18:7).