Low Voltage versus Mains Lighting in the Garden

The advantages of mains voltage lighting are often plain to see, but some of the benefits of a low voltage lighting scheme are less well understood. Here are some of the main points to consider.

Mains Voltage

Mains voltage systems are well understood by electricians, as they are usually familiar with 240 volt wall and ceiling lights and exterior lanterns. They may be unfamiliar with and therefore shy of low voltage installations in the garden and will try to put you off. The main advantages of 240 volt installations are,

  1. No need to use transformers
  2. Easier installation of wall spotlights where hiding transformers can be difficult.
  3. You don’t need to pay such close attention to voltage drop in 240 volt cables as you do at 12 volt
  4. Uplighting of l0arge trees often requires use of energy efficient metal halide lights which all run at 240 volts 

One of the main disadvantages is that nearly all the 240 volt cables in the garden must be armoured and/or have some other suitable protection against accidental damage. Only the last 2 metres to the light can be a flexible cable. This results in more ugly junction boxes and less flexibility. Another big disadvantage is that 240 volt lamps blowing will often trip out a circuit breaker, whereas this rarely happens with 12 volt lamps as the current surge is absorbed by the transformer.

Using a single RCD for large numbers of 240v fittings is not recommended due to the risk of nuisance tripping. We advise the use of separate RCD protection for each circuit and a maximum of 12 fittings per RCD. Where a garden lighting installation of more than 12 spike mount or recessed lights per circuit is proposed, we suggest the installation of 12v lights with transformers, which results in a significantly higher fault tolerance and reliability in the total installation

Low Voltage

Once you have accepted that you will need transformers there are many benefits with low voltage lighting.

  1. Safety – 12 volts is inherently safe for children and pets
  2. A bigger range of good quality, smaller fittings to choose from.
  3. Easier installation of cables in borders and planting – flexible cables to spike spotlights can be several times longer than to 240 volt garden lights and you can move them around more easily.
  4. A better range of lamps to choose from which are brighter, whiter, more efficient and longer lasting than their 240 volt cousins. Some 12 volt lamps are twice as efficient as their 240 volt equivalents.
  5. If you have an accident with a low voltage cable it is usually easier to fix.
  6. Low voltage transformers and power supplies absorb transients such as those caused when a lamp blows and are, to a degree, tolerant of earth currents arising from a bit of damp in light fittings. A little bit of dampness might not affect a 12 volt circuit but it could render a 240 volt circuit unusable.

It is possible to use both 240 volts and 12 volts together in the garden – the only difference is that instead of just a junction box there is a transformer there as well. 240 volt GU10 lamps are not as bright as the 12 volt MR16 lamps but they have a warmer quality, which might suit some situations better than the crisp look of low voltage lighting. Conversely you might need the low voltage crispness to bring out the best in foliage.

Electricians sometimes say they don’t want to use 12 volt lights because they have had problems with transformers in the past, but this is usually related to interior installations where poorly sited transformers have overheated in insulated locations, the use of older types of transformers in enclosures which were not as fully weatherproof as modern types, or condensation getting into electronic transformers which were not potted for outside use. The wide range of both magnetic and electronic transformers suitable for use outside really undermines this argument.

Copyright 2014; Information based on products supplied by Lighting for Gardens Limited and is advisory only. The company accepts no responsibility for incorrect use or application of information given. Light fittings can become hot in use; exercise appropriate precautions. Exterior electrical installations should be undertaken by a qualified electrician.