Light Center Length. The distance from an arbitrary point on the lamp's base to the center of the filament. One of the more important specifications of stage/studio lamps. For example, the ANSI EGG and BTN lamps both have medium prefocus bases, similar wattage, color temperature, and life, but their LCLs are drastically different, making the two NOT interchangeable. The EGG is used in the radial ERS and the BTN in the 6" Fresnel.