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Q. How many garden lights can I run from one transformer?
A. In fact, garden lighting transformers are available in a wide range of wattage ratings, so we need to look at the question in reverse: “what size of transformer do I need to power a group of garden lights”? This is simply a matter of multiplying the wattage and numbers of the lamps (bulbs) used in the garden light fittings (or “luminaire” as they are called in the professional lighting trade) to be connected to the transformer. In most cases we need to consider some spare capacity within the transformer rating so that we have scope to increase some lamp wattages as plants grow, or to allow for some flexibility in adding an extra spotlight or other garden light in future. This helps the garden lighting to “grow” with the garden. Have a look at Help sheet No. 2: Calculating garden lighting transformer size
Q. My lights have condensation on the lenses – what can I do about it?
A. All exterior lights, especially IP68 lights, are prone to condensation inside if they have been fitted during weather conditions which mean damp air has been trapped inside; a few drops of condensation on the underside of a lens is often mistakenly exaggerated as water getting into the light on a larger scale. If this has happened, dry the interior of the fitting with tissue, then stand the light out of water facing vertically upwards with the lamp and lens fitted but without the top plate in place; switch the fitting on for 15-20 minutes so it warms up enough to dispel any moist air. Switch off and screw the top plate in position, having either waited for the fitting to cool to a temperature suitable for safe handling or wearing thermally insulated gloves.
Q. Water is getting into my lights – why?
A. You may be using the wrong light in the wrong place or the problem may be caused by incorrect installation or maintenance – have a look at Help sheet 11: IP ratings – Weatherproof or waterproof?
Q. What size of transformer do I need to power a group of garden lights?
A. This is simply a matter of multiplying the wattage and numbers of the lamps (bulbs) used in the garden light fittings (or “luminaire” as they are called in the professional lighting trade) to be connected to the transformer. In most cases we need to consider some spare capacity within the transformer rating so that we have scope to increase some lamp wattages as plants grow, or to allow for some flexibility in adding an extra spotlight or other garden light in future. This helps the garden lighting to “grow” with the garden. See Help sheet No. 2: Calculating garden lighting transformer size.
Q. What is the difference between a transformer and a power supply ?
A. A transformer provides alternating current (a.c.) output of 12 or 24 volts; 12 volts a.c. is normally used to power halogen lamps in low voltage garden lights. A dc power supply provides direct current (d.c.) output (same as a battery) and is required for some light emitting diodes (l.e.d.s), such as linear led lighting for example. L.e.d.s consume a lot less power than incandescent lamps and are generally less sensitive to small voltage reductions but note that l.e.d.s are vulnerable to overvoltage, so you should generally use a regulated 12 volt DC power supply to ensure stable voltage to a small group of led lights. Help sheet No. 3 l.e.d. transformers will help you further
Q. How much low voltage cable do I need?
A. How long is a piece of string?!!!!! A lot will depend on the combination of lights and cables you are using. For most installations 2.5mm2 cable is the general purpose choice (T9912 - 50m pack; T9913 - 25m pack) and allowing 8 metres of cable per light is a good rule of thumb for the amount you will need unless there are special circumstances. Always allow 1m loop of slack cable for spike spotlights curled up by the transformer to allow for flexibility in positioning. Allow the same when wiring moonlighting downlights or spotlights in trees to allow for growth.
Q. What length of cable can I use from the transformer to a garden light?
A. “Cable voltage drop” occurs in all electric cables, but in a 12 volt garden lighting system special care must be taken to limit this to avoid loss of light output resulting from voltage reduction at the lamp. Some manufacturers recommend a maximum of 1 volt drop, but this would result in a loss of 30% of the rated light output of a halogen lamp - a 50 watt lamp would only give 35 watts worth of light. The loss of voltage is higher the longer the cable run and the higher the lamp wattage. To limit this loss of light output, keep cable voltage drop to under 5% (0.6 volt in a 12 volt system) by sticking to shorter cable runs wherever possible. Help sheet 5 Low voltage cabling layout for halogen garden lights will help you work out your cabling layout. Led lights are subject to different considerations, as explained in Help sheet 4 - Low voltage cabling layout for led garden lights.
Q. Can I run longer cables to l.e.d. (light emitting diode) lights compared to halogen lights?
A. Yes. L.e.d.s consume a lot less power than incandescent lamps and are generally less sensitive to small voltage reductions, so cable runs can also be a lot longer. Note that l.e.d.s are vulnerable to overvoltage, so unless you are using an l.e.d. garden light like Barrel/Rebel spotlights, which are made especially to work from a wide range of both AC and DC voltages, you should generally use a regulated 12 volt DC power supply to ensure stable voltage to your l.e.d. deck lights, recessed uplights or steplights. See Help sheet 4 - Low voltage cabling layout for led garden lights and Help sheet 3 - l.e.d. transformers.
Q. “How often would my housekeeper have to polish those?”
One lady looking at copper lights at the Chelsea Flower Show was heard to ask this and enquired about lacquering them to stay shiny – lacquer won't last forever, but do you really want shiny copper lights in your garden? Copper garden lights typically weather to a mottled brown finish to blend with brickwork, bark mulch, woody planting and timber. Weathered copper spreadlights, for example, are the most popular of this type of light fitting as their weathered appearance looks much more natural in the garden than any other metal or painted finish. See Help sheet 13 for more information on "Weathering of natural finishes". Copper spotlights are likewise popular for their discreet, weathered appearance in gravel or bark mulch. Weathering will typically take 4- 8 weeks depending on the weather.