Solutions of hydrochloric acid caused the light bulb to glow brighter than solutions of acetic acid. how do you account for the difference in behavior between these two compounds?

The primary difference between hydrochloric acid and acetic acid is that hydrochloric acid undergoes a complete ionization, whereas acetic acid does not. This is why a light bulb will burn brighter in the solutions of hydrochloric acid, and also why hydrochloric acid is considered a strong acid, while acetic acid is considered a weak acid.