This is a high quality lamp as fitted as standard in the Hella Marine, AquaSignal and other quality navigation light fixtures. These lamps are well designed and use rough service tungsten filaments which are adequately supported and engineered to maximise longevity in the marine environment. 

To meet COLREG distance visibility requirements it is recommended that a 10W lamp is used in Anchor, Steaming and stern lights and a 25W lamp in Bi Colour, Tri Colour and Port and Starboard Lights. , 

‘Standard’ incandescent bulbs, produce light by heating a tungsten filament until it is white hot. Over time, incandescent bulbs will become progressively less bright as the filament slowly evaporates. Tungsten residue settles on the inside of the glass envelope and reduces light output. Lamps should be regularly replaced as they approach the end of their working life..   

It is recommended that port and starboard lamps are replaced as pairs as often when one lamp fails others of a similar vintage are likely to fail soon afterwards.