Why Even Spacing Beats More Bulbs

The quickest way to make a festoon display look untidy is to fix the cable first and think about the bulbs afterwards. Light falls away with distance, so a bulb sitting 40cm from its neighbour creates a bright pool, while a 1.5m gap reads as an unlit stretch of nothing. Neither problem is solved by buying more bulbs — it is solved by spacing them properly across the whole run.

In a well-balanced display, the pools of light overlap just enough that the eye reads a continuous ribbon rather than a series of dots. That happens when the distance between bulbs is roughly two to three times the diameter of the glow they throw. A standard 4.5cm golfball bulb gives a soft pool of around 1.5m at knee height and considerably more at ground level, which is why spacing between 50cm and 1m is the practical sweet spot for most gardens.

Measure the Run Before You Order

Festoon sets are sold in fixed lengths with a fixed number of sockets, so your spacing is largely decided the moment you choose a set. Before you buy anything, take a tape measure to the space and work out two numbers: the total distance you want to cover, and the mounting height.

• Run length: measure along the path the cable will actually take, not the straight line between two anchor points. A sagging cable is longer than the span it crosses.
• Mounting height: measure from the fixing point down to the surface you want lit — usually a patio, decking or table.
• Anchors: note where wall hooks, pergola beams, fence posts or trees will take the cable. Each change of direction eats into your usable span.

As a rough rule, a low-voltage festoon set with sockets every 50cm gives a bright, sparkly look, while sets spaced at 75cm or 1m feel calmer and more architectural. A 10m set with 20 bulbs is spaced at 50cm; a 20m set with 20 bulbs is spaced at 1m. Check the specification rather than assuming, because two sets of identical length can differ enormously.

Finding the Right Bulb Interval

Work backwards from the effect you want. If you are lighting a dining table or a seating nook where people will sit underneath, closer spacing — around 60cm — keeps faces lit evenly and avoids shadows. For a long boundary run viewed from a distance, 90cm to 1m looks more elegant and uses fewer bulbs, which matters if you are running from a transformer.

A worked example helps. A 9m pergola beam, lit at 75cm intervals, needs 13 bulbs (12 gaps plus the first bulb). The same beam at 50cm intervals needs 19. That is a difference of six bulbs, roughly 9W at 1.5W each, and a noticeably different feel. Neither is wrong — but you need to know which one you are ordering before the box arrives.

Bulb size matters too. Chunky 8–10cm globes can carry a wider interval of 1m without looking sparse. Slim, small bulbs at the same spacing look mean. If in doubt, go slightly closer than you think you need.

Spacing on Pergolas, Patios and Awkward Corners

Straight runs are easy. Corners and level changes are where displays fall apart.

• Pergolas: run cables along the beams rather than across the rafters if you want an even wash over the seating area. Spacing measured along the cable will feel tighter once the cable sags, so allow a little extra room.
• Patio walls: mount at 2.2m to 2.5m and space bulbs at 75cm. Lower than 2m and the bulbs become obtrusive; higher than 3m and you need closer spacing to compensate.
• Zig-zag runs: keep the interval consistent along the cable, not per straight section, or the corners will look crowded and the middles empty.
• Fence lines: a gentle single swag between posts spaced at 1m per bulb is the classic look. Two swags between the same posts halves the effective spacing and doubles the brightness.

Also consider the first bulb. If your set begins with 1m of plain cable before the first socket, plan for that dead length at the plug end, ideally tucked behind a post or shrub where it will not be noticed.

Cable, Sockets and Practical Limits

Festoon sets are usually connectable, but the total number of bulbs you can run from one plug is limited. Lower-wattage LED bulbs draw around 1W to 2W each, so a typical 20-bulb set pulls 20W to 40W. Add the transformer's overhead and you may find you can safely link two or three sets before you need a second power source.

Spacing also affects weight and sag. Wider intervals mean fewer bulbs and less strain on the cable, but also more sag over long spans. For anything over 6m between supports, a tension wire or guide rope takes the load and lets you set the swag deliberately rather than letting gravity decide.

Fine-Tuning Once It's Up

Hang the run loosely first, stand back in the evening, and look for the bright pools and dark gaps. Adjusting the sag is often all that is needed: a deeper swag bunches bulbs towards the middle and opens them out at the ends, which is useful if a central seating area needs more light. Shallower spans spread light more evenly.

If one stretch is still too dim, resist the urge to add a whole extra set. A short extension or a single additional bulb on a clip often solves the problem for a fraction of the cost. Plan the spacing before you order, and the display will look considered rather than improvised.