Don's bulbs rare light bulbs and lamps glossary of terms definition of: LIGHT CENTER LENGTH What is LIGHT CENTER LENGTH? LCL is Light Center Length. LCL is the measurement from the base plane to the middle of the filament (or light field if not a Filament bulb). Base plane depends on base type. Refer to Bulb base photos on my website for LCL measure from points. references for this page: LIGHT CENTER LENGTH, LCL