Corrosion protection is possibly one of the most overlooked but crucial bits of information needed when judging suitability of a product. ISO12944 is the industry standard for corrosion protection by protective paint systems. Ratings are categorized from C1 for dry or cold environments with very low pollution to CX (formerly C5-M) for extreme industrial areas and offshore areas with salt spray.
A durability category ranging from Low (7 years) to Very High (>25 years) is also part of ISO12944.
This durability rating is important, particularly in the context of temperature fluctuation. There are many ways that temperature can accelerate corrosion in exterior or humid environments. Expansion and contraction of parts is a concern, particularly when materials with dissimilar rates of thermal expansion are assembled and combined to form a watertight seal. There are various gasket solutions to account for this expansion or movement, but all solutions have a time horizon which needs to be factored into a maintenance schedule. Gaskets will fail over time and this leads to ingress.
But a primary concern with corrosion from temperature fluctuation is internal humidity and dew point. Condensation of water can prematurely corrode the internal surfaces of a luminaire when dew points are crossed during temperature and atmospheric humidity fluctuations. One way of combating this is to seal and fill internal cavities with an inert and non-moisture bearing gas like nitrogen. There are difficulties with this solution in both manufacturing and servicing. And it’s often impossible to verify when a seal failure has occurred.