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How many deck lights you need, where they go, and what the whole system costs.
With these inputs:
| Result | Value |
|---|---|
| Fixtures needed | 19 |
| Estimated cost | $457 – $1,087 |
| Transformer | 30 W |
| Low-voltage wire | 96 ft |
| Stair and step lights | 4 |
| Post cap lights | 8 |
| Under-rail strips or pucks | 7 (one per 6 ft of 40 ft railing) |
| Total load | 23 W — transformer sized at 80% capacity |
| Fixtures | $344 – $842 |
| Transformer | $60 – $130 |
| Wire and connectors | $53 – $115 |
Size the transformer to about 80 percent of its rating so it runs cool and leaves headroom to add fixtures later — 23 watts of load points at a 30 watt unit. Run the wire before the decking goes down if you possibly can; retrofitting under a finished deck is the expensive part of any lighting job. Low-voltage systems are DIY-friendly in most jurisdictions, but the transformer still needs a GFCI-protected outdoor receptacle, and that part is usually an electrician's work. Prices are national estimates for LED fixtures.
Deck lighting is sold by the fixture but planned by the position: stair risers, post caps, under-rail strips and recessed floor lights each have their own spacing rule. This counts the fixtures your deck actually needs from its dimensions, sizes the transformer, and prices the wire and labour alongside them.
Work from positions, not a total. One light per stair step or per riser, one per railing post if you want post caps, and one under-rail fixture every 6 ft of railing. A 16 by 12 ft deck with four steps and eight posts comes to about 19 fixtures for the usual package. Recessed floor lights, if you add them, go roughly one per 40 square feet.
Add up the wattage of every fixture and size the transformer so that total is about 80 percent of its rating. LED deck lights draw roughly one watt each, so 19 fixtures is around 23 watts — a 30 watt transformer covers it with a little spare. Leaving headroom matters because people almost always add lights later.
A DIY low-voltage package for a typical 16 by 12 ft deck with stairs and eight posts runs about $500 to $1,200 for fixtures, transformer and wire. Having an electrician install it adds roughly $600 to $1,300 on the same system. Recessed floor lights and integrated riser lights sit at the top of those ranges.
Yes, but plan the routes first. Post caps and surface-mounted stair lights are straightforward because the wire runs along the underside of the rail or the stringer. Recessed floor lights and under-rail strips are much harder after the fact — the wire has to come up through the frame, which usually means working from below or lifting boards.
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