This paper reports on a systematic and quantitative assessment of light induced degradation (LID) and regeneration in full Al-BSF and passivated emitter rear contact cells (PERC) along with the fundamental understanding of the difference between the two. After LID, PERC cells showed a much greater loss in cell efficiency than full Al-BSF cells (similar to 0.9% vs similar to 0.6%) because the degradation in bulk lifetime also erodes the benefit of superior BSRV in PERC cells. Three main regeneration conditions involving the combination of heat and light (75 degrees C/1 Sun/48 h, 130 degrees C/2 Suns/1.5 h and 200 degrees C/3 Suns/30 s) were implemented to eliminate LID loss due to BO defects. Low temperature/long time (75 degrees C/48 h) and high temperature/short time (200 degrees C/30s) regeneration process was unable to reach 100% stabilization. The intermediate temperature/time (130 degrees C/1.5 h) generation achieved nearly full recovery and stabilization (over 99%) for both full Al-BSF and PERC cells. We discussed the effect of temperature, time and suns in regeneration mechanism for two cells.