Lampy letting himself get hit by lightning to supercharge the battery, allowing the others to survive. He doesn't die but his bulb is shattered.
While the other appliances are all dedicated in their own right to find the Master, few are as devoted to finding him as Blanky. Near the end when the Master finds them in the dump Blanky is the first one he spots and what does he do? He snuggles him like he was a kid again. Given how much crap the gang had gone through at that point and how much emphasis has been placed on Blanky's love of the Master, it's not hard to imagine how Blanky must have felt at that point.
In the Polish dub of 'City of Lights', Lampy's line as they're going through the tunnel is 'When darkness is all around, I'll beam light". It fit well with the scene and it's a sweet translation from the original line as well.