Exterior Lighting That Survives Salt Air

Fixtures fail faster here than the catalog suggests, and they fail in a particular order: the fasteners first, then the gasket, then the finish at the edges and around the screw bosses, and only last the body everybody was worried about. If you specify for the body and let the supplier pick the hardware, you have specified the wrong half of the fixture.

This page is what I have learned specifying exterior lighting a few hundred yards from the Atlantic. It is written for specifiers, contractors and property managers, and it is deliberately specific, because vague coastal language on a cut sheet is how buildings end up with rust stains down the stucco.

What is actually attacking the fixture

• Chloride pitting. Salt chloride ions break down the passive film on stainless and aluminum locally rather than evenly, so you get deep pits rather than uniform thinning. For stainless the resistance to this is quantified by the Pitting Resistance Equivalent Number, PREN, calculated as chromium plus 3.3 times molybdenum plus 16 times nitrogen.
• Galvanic corrosion. Two dissimilar metals in electrical contact with salt-laden moisture between them form a cell, and the less noble one dissolves. A stainless screw in an aluminum housing is exactly this arrangement. It is worst when a small anodic area faces a large cathodic one.
• Crevice corrosion. Oxygen is depleted inside a tight gap while the surrounding air stays oxygen-rich. Chloride concentrates in the gap, the pH falls locally, and the metal dissolves at that point. Threaded fasteners, gasket seats, washers and overlapping surfaces are all crevices.
• UV on the polymer parts. Gaskets and lenses age in sunlight, and a gasket that has gone hard has stopped sealing, which lets the salt inside where you cannot rinse it off.

Materials, ranked honestly

Stainless: 316 is the floor, not the ceiling, and it is not fit-and-forget. The molybdenum content is the entire technical argument. Type 316 runs roughly 2 to 2.5 percent molybdenum where 304 has none, which puts 316 at a PREN of about 23 to 28.5 against 304 at about 17.5 to 21. The Australian Stainless Steel Development Association, which publishes the best public guidance on coastal atmospheric exposure, recommends grade 316 as a minimum within about five kilometres of surf. Hallandale Beach oceanfront is inside that band several times over. For splash zones and unwashed areas, duplex or super-austenitic grades rather than 316.

Surface finish matters nearly as much as grade. ASSDA recommends a surface roughness below 0.5 micrometres Ra. Matt and bead-blasted finishes hold deposits and need washing more often. Tea staining, the brown discolouration you see on coastal stainless, is cosmetic rather than structural, but owners do not experience it that way.

Wrought aluminum: ask for the alloy number. The corrosion-resistant families are the 5000 series, magnesium alloyed, and the 6000 series. There is no body that certifies the phrase marine grade, which means on a lighting cut sheet it is marketing until an alloy designation appears next to it. Make the alloy number a submittal requirement.

Die-cast aluminum: this is where cheap fixtures give themselves away. Copper in the casting alloy forms microscopic galvanic cells and sharply reduces corrosion resistance. Common import die-cast alloys A380 and ADC12 carry roughly 1.5 to 4 percent copper. Serious luminaire manufacturers already specify against it: a published Kim Lighting specification calls for one-piece die-cast low copper aluminum alloy 360 at less than 0.6 percent copper, with a minimum wall thickness. Under paint you cannot tell A380 from A360, right up until filiform corrosion starts at a screw boss two years in.

Copper, brass and bronze. Genuinely good coastal materials if the client accepts the patina, which develops brown within days and takes something like seven to nine years to reach the familiar green in a marine environment. Avoid high-zinc brasses, which dezincify.

The two spec lines that matter most

• Gaskets: silicone or EPDM. Both hold up under UV. Prohibit nitrile, which does not. Require the gasket to be field-replaceable and require the manufacturer to publish a replacement part number, because some coastal warranties are conditional on periodic gasket replacement and you cannot replace what you cannot buy.
• Lenses: tempered glass where you need the photometrics to still be true in fifteen years. Acrylic is acceptable with some yellowing. Polycarbonate only where impact is the governing risk, accepting a shorter life and crazing.
• Finish: specify the process, not the color. A chromate or chrome-free conversion pretreatment with a stated minimum etch weight, then AAMA 2604 as a minimum and AAMA 2605 for oceanfront, stating which edition you mean. Class I anodize at 0.7 mil minimum per AAMA 611 is the alternative.

How to read a corrosion claim on a cut sheet

"1,000 hour salt spray tested" on its own means very little. ASTM B117 is a description of apparatus and conditions. It contains no pass or fail criterion whatsoever, and ASTM itself states that prediction of performance in natural environments has seldom been correlated with salt spray results used as stand-alone data. A meaningful claim has three parts: the hours, the acceptance criterion, and the specification that sets it. For example, AAMA 2605 asks for 4,000 hours to ASTM B117 with a stated minimum rating at the scribe and a stated blister rating in the field. That is a claim. A bare hour count is not.

ISO 9227 is the ISO counterpart, with neutral, acetic and copper-accelerated variants, and carries the same honest caveat about correlation to real outdoor exposure. Its value is repeatable quality control, not service life prediction.

Name the environment with ISO 12944. A South Florida oceanfront facade is category C5, which the older 1998 edition called C5-M for marine. Writing "C5, formerly C5-M" is correct under either edition and stops the conversation about whether the site is really that bad.

The Florida requirement that has nothing to do with corrosion

Along the Broward and Miami-Dade coast, exterior lighting visible from the beach is regulated for the protection of nesting sea turtles, and this catches out-of-state specifiers constantly.

The rule is about wavelength, not color temperature. A compliant source emits light at 560 nanometers or greater with wavelengths below 560 absent. A 2700K warm white LED contains a great deal of energy below 560 nanometers and does not comply, however warm it looks to the eye. Amber and PC-amber sources do. Fixtures must also be kept low and fully shielded so the source is not visible from the beach.

In Broward, nesting season runs from 1 March to 31 October. The trigger is visibility from the beach rather than distance from it, so an upper-floor fixture or light bouncing off a pale wall can be in scope. Ordinances differ by municipality, and some are quite specific: Pompano Beach, for example, limits exterior pole and base fixtures to 48 inches off the ground. Florida Fish and Wildlife Conservation Commission maintains a certified wildlife lighting product list, and it is the sensible place to start.

Maintenance, stated plainly

Coastal stainless is a maintenance-dependent material. ASSDA suggests washing grade 304 in coastal areas that are not rain-washed three to four times a year where there are no deposits and up to twelve times a year where there are, using soap or a mild detergent and warm water followed by a clean cold rinse.

The practical version for a building: anything under a soffit or a balcony that never sees rain needs rinsing on a schedule, because those are precisely the fixtures that fail first. The ones out in the weather do better. Owners find this counter-intuitive and it is worth telling them at handover.

Common questions

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