Broken light bulbs. Remove a broken light bulb safely
When a light bulb has broken off inside it's fitting, make sure that the power is isolated and use something like a carrot or potato to push onto the broken glass so you can turn the bulb with safety
Also
Before breaking the stubborn light bulb that needs replacement try using the old standby WD40 lightly on the socket. Hint : When installing the new light bulb spray a little WD40 the threaded area