The bridge

This closeup shot of the extremity of an uncoated compact fluorescent lamp shows an interesting phenomenon which affects the electrical discharge when it passes through the bridge connecting both legs of the lamp. Charge losses are greater in that narrow section of the burner than elsewhere, causing the electric field in the discharge to increase, which results in a higher electron energy there than in the rest of the lamp. The consequence is that the excitation of the lamp's atmosphere changes significantly there, resulting in neon from the buffer gas to emit its characteristic red light whereas the rest of the lamp emits mercury's greenish-blue light.