IP Ratings for Outdoor Lighting: What IP65, IP66, and IK Ratings Really Cover

Every outdoor fixture datasheet leads with an IP rating, and most specifiers read it as a simple “weatherproof” checkbox. The rating system is narrower than that — and several of the failures that kill outdoor fixtures aren’t covered by it at all.

Reading the two digits

First digit — solids: 5 means dust-protected (some ingress allowed, no harm), 6 means dust-tight. Second digit — water: 5 is jetted water, 6 is powerful jets, 7 is temporary immersion, 8 is continuous immersion.

So for exterior luminaires:

• IP65 — fine for sheltered installation: under canopies, eaves, most wall-mounted positions.
• IP66 — the sensible default for fully exposed floodlights and area lights; survives driven rain and pressure-washing.
• IP67/68 — only needed for in-ground, fountain, or flood-prone installations.

What IP ratings don’t tell you

1. Impact resistance. That’s the separate IK scale (00–10). Car parks, sports courts, and low-mounted fixtures should carry IK08+.
2. Corrosion. A coastal site will destroy a poorly finished IP66 fixture. Look for C4/C5 corrosivity-class finishes or marine-grade alloys within ~10 km of salt water.
3. Condensation. Sealed fixtures breathe as they heat and cool; without a pressure-equalizing vent (e.g. a Gore-Tex membrane), humid air gets pumped in and condenses on the lens. This is the classic “IP66 fixture full of water” complaint — the rating was never violated.
4. UV and thermal aging of gaskets. Warranty length is your best proxy for gasket quality.

Indoor fixtures with outdoor ratings

IP65 shows up on indoor products too — high bays in food-processing plants get washed down, and dust-tight optics in warehouses stay cleaner, holding output between maintenance cycles. It’s a legitimate spec even with no rain in sight.

Quick reference