Nearly every failed outdoor LED strip installation fails the same way: water gets in at a cut end, tracks along the copper, and takes out the whole run within a season. The strip was sold as IP65 or IP67, so the installer believes the rating covered them. It did not, and this article explains exactly why — and what to specify instead.
What the IP number actually measures
IP ratings have two digits. The first is solids, the second is water. Neither digit says anything about sunlight, temperature cycling or salt — the three things that kill an outdoor strip before water does.
| Rating | Water test | Often misread as |
|---|---|---|
| IP65 | Water jets from a nozzle at 12.5 l/min, 3 m, 3 minutes | “Fine outdoors” — it is not, in wind-driven rain against a joint |
| IP66 | Strong jets, 12.5 mm nozzle, 100 l/min | “Better than IP67” — it is not; different test |
| IP67 | Immersion 1 m for 30 minutes | “Permanent underwater” — 30 minutes is not permanent |
| IP68 | Immersion beyond 1 m, duration agreed with manufacturer | Varies wildly; the standard does not fix the depth or time |
That last row matters more than people expect. IP68 is manufacturer-defined, so one supplier’s IP68 may be 2 m for 24 hours and another’s may be 1.5 m for one hour. Always ask for the actual test condition, not the number.
Four ways an IP67 strip still fails outdoors
1. The cut end. This is the big one, and it accounts for most of the returns. A factory extrusion is sealed; the moment you cut it to fit and crimp on an end cap, the rating belongs to your workmanship, not the factory’s. Silicone and heat-shrink on site gives you something closer to IP65, and it will not survive two winters of thermal cycling.
2. Condensation. A sealed tube installed in a cold climate pumps moist air in through any imperfect seal as it cools overnight, and that moisture condenses on the inside of the jacket. The strip corrodes from within, with no visible water at all. This is why vented profiles and weep holes exist — an airtight enclosure outdoors is often worse than a drained one.
3. UV. PVC jackets yellow and embrittle under UV, and silicone resists it far better. A strip in a south-facing location in Spain or Florida sees enough UV to change the jacket’s transmission and mechanical strength within two to three summers. No IP rating tests this.
4. Thermal cycling at the fixture. An aluminium channel expands and contracts differently from the silicone jacket bonded into it. Over hundreds of cycles the bond fails, water enters, and the run dies in a place that is invisible until it is dark.
The four “IP65” constructions you will meet
- Silicone tube — the strip slides into an extruded tube, ends sealed. Good general outdoor performance, but the seal is only as good as the cap.
- Silicone pour / potting — the strip is embedded in a continuous silicone coating. Better than a tube at the body, still vulnerable at the cut.
- Glue-coated (epoxy dip) — cheapest, yellows fastest, cracks under thermal cycling. Avoid outdoors.
- Fully encapsulated — overmoulded ends, no field cutting. The only construction that is genuinely IP67 or IP68 at a joint.
If a project genuinely needs the strip to survive wet conditions, the answer is not a better sealing method on site. It is factory-sealed lengths in the exact size the installation needs, ordered to millimetre and never cut.
What to ask for instead of an IP number
Four documents separate a strip that lasts five years outdoors from one that lasts one season:
- IP test report that tests the assembled product with end caps fitted — not the bare reel
- UV ageing data, ideally 500 hours of QUV or equivalent, with mechanical results after exposure
- Salt spray report, 96 hours minimum, if the site is within a few hundred metres of salt water
- Thermal cycling between operating extremes, which is what actually breaks bonds and seals
Installation details that decide the outcome
Even a well-made strip fails on a badly detailed installation. Use a drip loop at every vertical transition so water runs off rather than into the strip. Drill weep holes at the low end of any sealed channel. Keep end caps at the high point, never the low point. Mount so the strip is not standing in a pool of water on a flat surface. Where the run passes through a wall, use a gland rather than silicone.
Run the strip slightly below its rated power where possible. A strip at 12 W/m runs cooler than the same strip at 16 W/m, and every degree of junction temperature reduction translates into less seal degradation and longer life. Profiles do double duty here: the aluminium profiles that carry the strip are also the heatsink, and a strip in a profile typically runs 10–15 °C cooler than the same strip free-hung.
Practical specification for a five-year outdoor life
| Requirement | Minimum | Better |
|---|---|---|
| Jacket material | Silicone | Co-extruded silicone with UV stabiliser |
| Sealing | Factory-sealed lengths | Overmoulded ends, no field cutting |
| IP rating | IP67 with end-cap test report | IP68 with stated test depth and duration |
| UV ageing | 300 h QUV, no cracking | 500 h with mechanical retention data |
| Salt spray | — | 96 h, coastal sites only |
| Mounting | Aluminium channel with weep holes | Channel plus drip loops at every transition |
Compliance note for US and EU projects
Outdoor installations in the US typically fall under UL 2108 for the low-voltage system, with the driver under UL 8750 or UL 1310 for a Class 2 supply. In the EU, EN 60598-1 governs the luminaire, EN 62471 covers photobiological safety, and the ErP regulation applies to the finished product. An IP rating is not a substitute for any of these, and an inspector will ask for the file number, not the datasheet headline.
Checklist before you order
- Is the installation wet, damp, or merely humid? Damp is not wet, and specifying for wet costs money
- Will the strip be cut on site? If yes, accept IP65 at the joint and plan for it
- Can you order factory-sealed lengths instead? This is almost always the cheaper long-term answer
- Is the location UV-exposed on a south or west face? Specify silicone, not PVC
- Is it coastal? Ask for salt spray data
- Who is sealing the ends, and what are they using? Put it in writing before install
We supply silicone-jacketed strip and factory-sealed outdoor lengths with IP test reports that cover the assembled product and its end caps, plus the aluminium profiles and connectors that go with them. If you send us the location, mounting detail and expected life, we will tell you honestly whether IP65 is enough for that site — and if it is not, what to buy instead.