Fluorescent lamp with protected cathode to reduce end darkening

摘要

A low-pressure mercury vapor discharge lamp (10) includes a tubularly-shaped envelope (12) sealed at each end with a stem assembly (14). A fluorescent coating (26) is disposed on the interior surface of the envelope (12) and an electric discharge sustaining fill gas is provided within a hollow interior (24) of the envelope (12). Each stem assembly (14) includes a glass base portion (30) which seals the end of the envelope (12), an electrode (16), and a tubularly-shaped, light-transmissive, glass shield (22). The electrode (16) is disposed within the envelope (12) such that an electric discharge occurs between the electrodes (16) upon operation of the lamp (10). The glass shield (22) extends past the electrode (16) to partially surround the electrode (16) and shield the interior surface of the envelope (12) from material ejected from the electrode (16). The glass shield (22) allows the electric discharge to unaffectedly pass through an open end (42). Structural variations for supporting the glass shield (22) are also disclosed.