Contemporary low voltage garden lighting requires just three parts: a 12v transformer to provide a safe low voltage power supply; a cable to distribute the power supply to where it’s needed; and the garden light fittings.

First though it is vital to select which type of lighting (traditional incandescent bulbs or LEDs) and to gauge the rating of the transformer necessary to run the lights (which depends on how bright they are and how many are required).

We will cover the differences between the two types of system (and how to combine them) later, but both otherwise follow exactly the same basic principles.

Calculating the size of transformer required is simply a matter of counting up the wattages for all the actual lights (so, 3 x 10 watt deck lights plus 2 x 20 watt standard lanterns comes to 70 watts for example) and tells you what rating of transformer you need to purchase.

The transformer input is connected to a mains outlet and must therefore be placed inside. The transformer output is then connected to the cable which then leads outdoors.

The cable itself applies a load to the system, in addition to the load created by the light fittings, which you should allow for when calculating the correct transformer size. This is typically stated on the packaging and increases in line with the cable length, which imposes an effective limit on the length of cable.

It’s simple to determine whether a cable is too long since the lights are a) not as bright as they should be and b) discernibly dimmer the further away from the transformer they are. An effective remedy involves looping the cable (or running additional cable) back to nearer the transformer. It is imperative though that you do not cross-connect the two strands of wire that make up the cable - there is typically some type of marking on one of the strands so you can easily observe polarity.

When your cable has been connected and laid out, attach each low voltage garden light fitting in turn by cutting the cable near to where the fitting is and connecting it back with the light’s own cable also attached.

As noted above, both LED and conventional incandescent garden lighting are now widely available, and it can be confusing to know which to get and how to combine the two different types.

LED lights use considerably less power and do not generate any heat. They also produce much crisper, sharper light compared to incandescent lamps, which can be used to good effect or can look rather harsh depending on the effects you’re after.

With few exceptions, you should not attach LED lights to a regular low voltage garden system, or the other way around. What will happen is that either the lifespan of your LED lights will be cut to just a week or so, or the constant voltage transformer (LED driver) will suffer a similar fate.

There are of course some exceptions; some LED light fittings are designed to be used with a normal low voltage system and will state as much on the packet. But in most cases, in order to combine LED and incandescent 12v garden lights requires the use of 2 distinct cables, with one attached to a normal transformer and the other to a 12v LED driver, and with each type of light fixture connected to its relevant cable.

There are many benefits in running both types of garden lights; LED lighting has particular properties that enhance the range of possible lighting effects, and when used in tandem both types of lighting can be made to either contrast with or complement each other and so create effects that would simply not be achievable with just one or the other.