bulbs gas gas bulbs gas storage industry Rotterdam symmetry base bulb cap cost current double-contact-bayonet-base edison-screw-base electric-current electricity embedded-wires emissions filament gas-discharge globe glow glowing incandescence incandescent-light instant-start lamp light light-source lighting luminosity luminous luminous-efficacy sleeve standard stem traditional ultraviolet ultraviolet-emissions ultraviolet-light ultraviolet-radiation