In-ground uplighting is one of the most contentious lighting details in the designer’s tool box. It’s one of those things that brings out the amateur astronomer in everyone, as it scatters its light into the night-time sky. Uplighting adds to light pollution in the city and signals the presence of the willfully selfish in the countryside. Though it has to be said, its visual impact can be stunning.
But there is a dark side, literally, to the in-ground uplight, and one that would bring cheer to the supporters of the dark sky movement. This is the in-ground uplighter’s propensity to fail on a regular basis. It really is one of the most irritating pieces of lighting technology around.
Here’s the seven biggest headaches, and the fixes…
The problem: Water gets in from below
This is the number one problem with in-grounds. Physics tells us that things expand as they heat up, including the air inside an in-ground uplighter. Think of the fixture as a sealed reservoir of air that is then heated. The source of heat may be the light source, and even a ‘cold running’ LED produces some heat, or the heating may occur during the day as a result of solar gain. The air inside the fitting will expand and will look for an exit, be it through the diffuser gasket at the top or the cable gland at the bottom. This, however, is not the problem. The problem occurs when the fixture starts to cool down. As the air cools, what with nature abhorring a vacuum, the fixture will try to suck air back into itself. This is the beginning of the problem.
Out of sight is out of mind, unless you’re the supplier of equipment that requires cable terminations to be made by the installation contractors. Site-fitted glands, whether rated at IP68 or not are at the mercy of the person with the grips and this is something that should be avoided.
The best remedy is to select fixtures that come supplied with a factory-fitted cable and gland that ensures that water cannot be pulled into the housing either between cable and gland or gland and housing.
The second-best remedy is to make-off cable connections in a workshop and deliver the fixture to site with all cables and glands already in place. This is not ideal, but it helps in those situations where the installer is obliged to fit all of the cables. Try not to use plastic glands because there is always the temptation to overtighten which can damage the thread and compromise the seal. Rather, use a stainless steel gland, rated to IP68, which is far more resilient. And using a sealant around a cable gland is simply a pre-emptive declaration of failure in the quality of the gland and/or workmanship.
Water ingress into the bottom of the uplighter can also arise because the fixture sits for long periods in a bath of water. While some soils act as effective soakaways, others, like clay, can act as a reservoir. Type of soil can hold onto water long after the surface water has disappeared and can compromise the fixture. And its worth acknowledging that IP ratings may be time-limited; IP67 (immersible to 1m) at 30 minutes and IP68 (submersible) at the discretion of the manufacturer.
Photo credit: iGuzzini UK
The best way to stop water getting in from below is to ensure that the in-ground fixture is surrounded by appropriate soakaway material. If we accept that many uplighters will be mounted in paviors, it’s not acceptable to leave a void space beneath the pavior because of the risk of it breaking under mechanical load. Rather, the space around the uplight needs to be filled with rubble (coarse at the bottom, finer at the top) that allows water to build up during rain and then soak away into the ground beneath. But if it’s a deep clay soil then it may be best to abandon the lighting detail.
Again, manufacturers will advise on the recommended volume of a soakaway around their in-ground fixtures.
While we’re underground, there’s an associated issue to bear in mind. Even though its best to avoid making on-site electrical connections inside the uplight, on-site electrical connections still have to be made. In-ground uplights rarely occur as individual fixtures; they tend to herd and there will usually be a line of them running along the base of a wall, or along a pathway.
The electrical cable supplying the uplighters needs to run the entire length of the installation, with a connection needed at each fixture. The best type to use is T-junction, whereby the cable supplying the line of fixtures is broken at each fixture to allow a third cable, from the fixture itself (the cable that was factory- or workshop-fitted, hopefully) to be connected.
Two types of T-junction are in common use; an IP68 junction box that accepts a number of cables, each fitted securely into the box using a compression gland. These boxes usually have a removable lid that can be opened again for maintenance purposes. The other type of junction is a resin-filled T-joint. The resin ensures that no water can leak into the joint, and this also makes it a once-only connection. If it fails, then it has to be cut out and lengths of replacement cabling fitted – requiring yet more cable joints, so its best to get it right the first time.
In all of these circumstances, its vital that a circular cross-section cable is used, otherwise the gland cannot grip evenly around the cable sheath. The cables supplying the run of fixtures should be protected from mechanical damage and this is typically achieved by using SWA (steel-wire armoured) cabling. The local cable from the fixture into the junction box may also be SWA but is more likely to have just a tough outer sheath.
The problem: Water gets in from above
If air can escape from around the gasket around the top diffuser, then air can be sucked back in the same way, except that the air may be water. Any rainwater that’s collected on top of the diffuser can be pulled into the fixture as the air inside the housing cools.
In very good fixtures, it’s possible that the mechanics of the gasket acts as well as a pressure cooker and contains the air without leakage, but this is not the normal state of affairs. It must be assumed that most in-ground uplighters will surrender to the internal air pressures and that the diffuser gasket will be breached.
Only select those fixtures that do not allow water to pool on top of the diffuser, which is usually caught by the raised edge of the bezel. Ensure that the glass diffuser is flush to the bezel or is slightly convex to allow water to run off its surface.
The problem: The cover glass breaks
Accidents happen, but preventive action can be taken at the outset. The obvious problem comes from under-estimating the likely mechanical loading onto a diffuser. Uplighters are mounted in ground that may be intended to be walked on or driven across. These factors must be taken into account when the scheme is planned.
It may be helpful to incorporate physical barriers into the architectural design that protect in-ground uplights from passing traffic, such as a step detail that lifts the installation above the general ground level. All good manufacturers of in-ground uplights will have information on the mechanical limitations of their fixtures.
The problem: The in-ground gets flooded
Occasionally, in-ground uplights find themselves underwater. This scenario is one that we expect is only going to happen more often as our towns and city centres find themselves inundated due to extreme weather.
Photo credit: Paul Nicholls, Flooding in Lowestoft
The remedy is straightforward in principle, but may be a little more complicated in practice; switch off the fittings until the floodwaters have receded and give the ground surrounding the fixture time to dry.
While the visual effect may be impressive, there is nothing good to be gained from allowing in-ground uplights to operate while they are underwater. It just makes the potential for water ingress that much worse. Most of them are not intended as underwater fixtures, rated at IP68 or not.
The problem: The in-ground overheats
It may not be water that causes problems with in-ground uplighters. Urban development in areas like UAE has resulted in growing concern over the high ambient temperatures that in-ground fixtures have to endure. Temperatures in Dubai reach over 40°C in summer months and even winter temperatures are regularly above 20°C. These temperatures do not take into account the effect of direct radiant heat from the sun, which is far higher. In these conditions, and given that most luminaires are tested at 25°C, it is incumbent on the specifier to make sure that the preferred in-ground fixture is capable of withstanding such conditions.
Photo credit: Place in the sun magazine 2011, Dubai
This lies with the manufacturers and it is essential to gain confirmation from the manufacturers that their equipment is fit for purpose in these kind of conditions.
The problem: Light spills into the sky
Any light that escapes to the sky is a waste of light and energy. It suggests that the design hasn’t been worked through and perhaps inappropriate fixtures have been chosen.
There are occasions when the impact of an uplight installation probably won’t make much difference to the overall light pollution problem, in city centres for example – but uplighters in the rural environment are a different proposition. The countryside is a dark place and a single in-ground uplighting installation can have dramatic effects on the local environment. In such a setting, spill light should be reduced to zero and any uplighting should be closely controlled in the way that light is distributed around the illuminated buildings and gardens.
As residential and commercial developments continue to spread into the countryside, it is surely time to consider the relevance of the uplighter and only use them with extreme care.
The simplest answer is to avoid uplighting as a component of a lighting scheme. Be a bit more creative, perhaps in the use of feature lighting.
If uplighting cannot be avoided then restrict the hours of operation; switch off domestic uplighting at 9pm or 10pm; switch off commercial uplighting at the end of business or at the same times as a domestic scheme.
If possible, locate uplighting within the structure being lit – within arches or under canopies, for example. And if that’s not possible because you’re lighting a wall, then use fixtures with asymmetric distribution that reduces unwanted spill light.
Consider the optics of the fixture. Do you really need a beam of light, or is it sufficient to produce a general glow and allow the inverse square law to do its work.
And maybe if you’re lighting in a garden, consider downlighting from within a tree crown rather than lighting upwards into it.
For more information on dark skies, please visit the website of the International Dark-Sky Assocation
The problem: The in-ground fails
Human interference deserves its own paragraph because stupidity can reign supreme in the matter of in-ground uplights and their installation. Most of what’s described below can be resolved by doing the job properly. It’s not too much to ask.
- cable glands not tightened
- cable glands not fitted (!)
- gaskets not cleaned before fitting
- up-lights fitted in the rain and not allowed to dry out
- cracked, chipped, broken diffusers ignored and fitted anyway
- incorrect cables being used (twin-earth, anyone?)
There is no doubt of the visual excitement that a good uplighting installation can bring to a building. It’s just a pity that so many installations fail because of poor specification and installation.
Photo credit: iGuzzini UK
Ah, possibly the most difficult fix of all, because we’re looking at the human condition. The best we can do here is encourage everyone concerned to appreciate the cost of getting things wrong, and so get things right in the first place.
The specifier needs to look at the quality of the fixture and not just how much it costs.
The installer needs to understand that, though it may be dry weather during the installation, that’s no excuse not to fit cable glands, just because there aren’t any to hand. It will rain and the electrics will fail.
The site supervisor needs to come to the party by keeping a weather eye open on things. A rainy day may not be the best time to install electrical fixtures in the ground if they have to be opened up.
And everyone needs to stand up and be counted if they think it’s OK to run twin-earth cable into a glanded fixture.
In-ground uplighting is completely unforgiving. Be certain of this: if the installation is faulty in any way, it will be found out.
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