IP Rating (Ingress Protection) (IP)
The IP code (IEC 60529) rates an enclosure’s protection with two digits: the first against solids, the second against liquids. IP65 is the practical baseline for outdoor and industrial lighting — dust-tight and resistant to water jets. The rating covers ingress and nothing else: it makes no statement about corrosion resistance, impact strength or explosion protection, each of which is a separate assessment.
The Two Digits
First digit — solids
| Digit | Protects against | Meaning in practice |
|---|---|---|
| 4 | Objects > 1 mm | Wires, small tools |
| 5 | Dust protected | Some dust may enter, but not enough to interfere |
| 6 | Dust tight | No ingress of dust at all |
The 5-versus-6 distinction matters wherever the airborne solid is the hazard rather than a nuisance: flour mills, feed plants, cement works, joineries. There, 6 is the floor.
Second digit — liquids
| Digit | Test | Meaning in practice |
|---|---|---|
| 4 | Splashing from any direction | Rain and splash only |
| 5 | Water jets, 6.3 mm nozzle, ~30 kPa | Hose-down cleaning |
| 6 | Powerful jets, 12.5 mm nozzle, ~100 kPa | Heavy-duty washdown, deck-level marine |
| 7 | Temporary immersion, 1 m for 30 min | Flooding risk |
| 8 | Continuous immersion, conditions agreed | Permanently submerged |
| 9K | 80 °C water at 8–10 MPa, close range | Hot high-pressure lance cleaning |
IP65 vs IP66 vs IP67 vs IP69K
This is where most specification errors happen, so it is worth being blunt about the differences.
IP65 is not a washdown rating. It is tested with a low-pressure 6.3 mm jet. A food plant, dairy or livestock building that pressure-washes its ceilings is operating well outside anything an IP65 fixture was tested against. IP66 uses a larger nozzle at more than three times the pressure and should be the floor wherever cleaning involves real pressure.
The digits are not a simple ladder. IP67 (temporary immersion) and IP69K (hot high-pressure jets) test different things, and one does not imply the other. A fixture rated IP69K is not automatically suitable for immersion, and an IP67 fixture is not automatically suitable for a steam lance. Where both matter, both must be stated — you will see markings such as IP66/IP69K.
| Environment | Sensible floor |
|---|---|
| Dry warehouse, workshop, plant room | IP65 |
| Outdoor floods, street and area lighting | IP65 – IP66 |
| Multi-storey and underground car parks | IP65 |
| Livestock and poultry housing | IP66 |
| Food processing, dairies, breweries | IP66 – IP69K |
| Cold stores and freezers | IP66 |
| Coastal, marine-adjacent, deck level | IP66 |
| Tunnels and underpasses | IP66 |
What the Rating Does Not Cover
- Corrosion. Salt air, ammonia in barns and chlorine in pool halls attack materials that shrug off water without difficulty. That is a material and fastener specification, backed by salt-spray testing — not an IP digit.
- Impact. Vandalism, forklift strikes and ball impact are the IK rating, a completely separate code.
- Explosion protection. A sealed fixture is not an explosion-proof one; ignition protection is a different engineering problem with its own certification.
- UV and ageing. A polycarbonate diffuser can yellow and lose output for years while the fixture remains perfectly sealed.
Why Fixtures Lose Their Rating in Service
The certificate describes a fixture as tested — new, correctly assembled, with its original gaskets and glands. Field failures come from four places:
- Gasket compression set. Cheap gaskets take a permanent squash and stop springing back. Silicone recovers; low-grade foam and EPDM do not.
- Cable glands. A gland is rated for a cable diameter range. A thin cable in a wide gland does not seal, whatever the fixture is rated to.
- Unused entries. An open or non-certified plugged entry is an IP20 hole in an IP66 body.
- Condensation, not leakage. A sealed fixture breathes as it heats and cools, drawing in humid air that condenses inside and cannot evaporate out. The fix is a hydrophobic breather membrane, not a tighter seal — see the tri-proof selection guide.
That last one is the reason a fixture can be genuinely IP66 and still have standing water inside after a year.
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