316 is a stainless steel alloy that adds 2 to 3 percent molybdenum to the standard 304 recipe. The molybdenum makes it far more resistant to pitting and corrosion caused by salt, chlorine and coastal air, which is why it is the grade used for boat fittings and outdoor lights near the ocean.

As a rule of thumb, homes within about 1 kilometre of the ocean should use 316 marine grade fittings, and anywhere salt spray can reach them it is essential. Between 1 and 5 kilometres from the water salt still travels on the breeze, so 316 stainless steel remains a smart upgrade for exposed positions. Pools are another trigger: chlorinated splash zones attack ordinary finishes the same way salt air does.

Both are corrosion resistant stainless steels. 304 suits sheltered inland use, while 316 adds molybdenum for much stronger resistance to chlorides, the salts found in sea air and pool water. If your lights will live near the coast or a pool, choose 316.

316 is highly corrosion resistant but not maintenance free. In coastal areas a light film of brown discolouration called tea staining can appear if salt is left to build up on the surface. It is cosmetic rather than structural, and a regular freshwater rinse keeps it away.

Look for IP44 or higher under a sheltered eave and IP65 or higher for walls, paths and gardens exposed to rain. Fittings recessed into the ground or washed by sprinklers should be IP67, and anything submerged, such as a pond light, needs IP68.

Wash the fittings with fresh water and a soft cloth every two to three months, more often on beachfront homes. A mild detergent removes salt build-up, and an occasional wipe with a stainless steel cleaner restores the finish. Avoid steel wool, scourers and chlorine based cleaners, which damage the protective surface layer.