Laser-induced spark technique is considered as a valid solution for performance improvement of igniters in aeronautical sector. By promising stable ignition of lean mixture in both high and low pressure conditions, its range of application spans from internal combustion to turbojet engines. In this work, the ignition characteristics of n-decane/air mixtures for different equivalent ratios (from 0.65 to 1.3) and initial chamber pressure (from 0.2 to 2.5 atm) are analyzed. For each condition, Langlie algorithm provides the incident energy E50 leading to a 50% ignition probability. The achieved results enable to define an empirical relation which predicts the absorbed energy by the ignition of n-decane/air mixture, as well as the energy threshold for each tested configuration. Moreover, flame shape development at E50 is investigated through image processing thanks to Schlieren recorded high-speed camera images.