Condensation in outdoor luminaires: causes and prevention

Why a sealed luminaire still fogs up

An outdoor luminaire is never hermetically sealed. There is air inside the housing, and that air contains water vapour. During the day a floodlight on a wall or column heats up from sunshine and its own heat, and the housing can become tens of degrees warmer than the outside air; after sunset it cools down. The air inside contracts, a slight vacuum forms and the luminaire draws in humid outside air through the gasket or gland. This is called breathing, and it happens with every luminaire, IP66 included.

When the inside of the glass or lens becomes colder than the dew point of the air in the housing, the vapour condenses as a haze or fine droplets. After a while in operation it usually clears again: the LEDs warm the housing and the moisture dissolves back into the air.

A light haze that disappears within an hour of switching on is therefore not a defect. Droplets that stay, a water line at the bottom of the glass or deposits on the circuit board are. In that case more water is getting in than breathing can remove, and the cause is almost always the gasket, the gland or the cable entry.

IP65 and IP66: what the rating does and does not tell you

The IP code describes protection against solid objects and water under test conditions. IP65 and IP66 are both dust-tight (first digit 6). The difference is in the second digit: 5 stands for water jets from a 6.3 mm nozzle, 6 for powerful water jets from a 12.5 mm nozzle at a much higher flow rate. In practice: IP65 is sufficient for rain, IP66 also keeps out driving rain and a pressure washer at a distance.

Neither rating says anything about water vapour, so an IP66 luminaire can fog up too. In practice, however, the seal of an IP66 luminaire is often more robust, so it usually exchanges less air and therefore less moisture. The street luminaires of VIA, the floodlights of FLUX and the post-top luminaires of POLARIS are IP66; in halls IP65 is the norm, as with ATRIA.

Rule of thumb:

• Under a canopy, a roof overhang or in an open shed: IP65 is enough.
• Exposed to rain on a column or facade: choose IP66.
• Car wash or food industry with close-range high-pressure cleaning: IP69K, such as the linear luminaires of TRIVO.

Gasket and screws: leaks often start at installation

The gasket is a ring of silicone or EPDM between the housing and the glass or cover. It only seals when it is compressed evenly all the way round. The most common mistakes: the gasket has jumped out of its groove on opening and has gone back in twisted, there is sand or a piece of cable sheath trapped under it, or the screws have been tightened unevenly so the cover sits askew.

Tighten cover screws crosswise, in two rounds and without an impact driver. A gasket that has been compressed for years has taken a set and no longer springs back; after maintenance, replace it rather than reuse it. Never drill extra holes in the housing for a sensor or bracket, and close every unused hole with a sealing plug.

Cable glands and cable entry

The cable gland is the weakest point. An M20 gland only seals with a cable diameter within the stated range, for example 6 to 12 mm. A cable that is too thin does not clamp, one that is too thick damages the sealing ring. If the luminaire has two entries for looping through, fit a blanking plug in the entry you do not use.

Bring the cable into the luminaire from below or with a drip loop, so rainwater runs away from the gland rather than towards it. On a street luminaire mounted on a 60 mm spigot the cable runs through the column; make sure the tilt angle is not so steep that the entry points upwards. The VIA luminaires are tiltable, so keep the entry horizontal or facing down.

Water also travels in along the cable itself, along the sheath or by capillary action between the cores. If the cable ends in a wet location, use a gel joint or a sealed junction box there. Inside the lighting column the connection belongs in a column cut-out box from NEXUS, not loose in the base.

Breather valve and pressure equalisation

Because breathing cannot be avoided, many outdoor luminaires have a breather valve: a membrane that lets air and water vapour through but blocks liquid water. The housing then breathes without a vacuum, so no moisture is drawn in through the gasket, and any moisture that does get in evaporates out again as the luminaire warms up.

If there are complaints, check that the valve has not been painted over, covered by a bracket or blocked with dirt. On a luminaire without a valve, one can sometimes be fitted in an unused gland opening; discuss this with us first, as any modification to the housing falls outside the IP test and may affect the warranty.

Step by step with a fogged luminaire

• Leave the luminaire on for an hour. If the haze clears, nothing is wrong.
• If droplets remain: isolate the supply, open the cover, inspect and clean the gasket and groove.
• Check the gland for cable diameter, tightening torque and drip loop, and close unused entries.
• Dry the housing and glass, refit or replace the gasket and tighten the screws crosswise.
• If the luminaire fogs up again afterwards, report it with photos via info@lichtplein.nl. VIA and FLUX luminaires carry a warranty of up to 5 years; together we will establish whether the cause lies in the luminaire or in the installation.

Frequently asked questions