Metal wire filament incandescent light bulb

This 5000 watt metal wire filament lamp was used in a searchlight. The bulb blackens on the inside because the filament gives off small particles while lit. To remedy this, coarse metal powder was added inside the bulb as a sanding agent. This allows the blackening to be removed from time to time. The service life of the filament is about 500 hours and this does not extend it.