Pitch, Rows and Watts per m²: One Number Sets All Three
Three decisions that feel separate — how many rows of strip a face needs, how many metres to buy, and how many watts per square metre the box will run at — are the same decision. They all fall out of one number: the pitch, the centre-to-centre distance between two rows.
The arithmetic, once
Each row of strip covers a band of face as wide as the pitch. In one square metre there are 1 ÷ pitch rows, and each row carries one metre of strip. Multiply by the strip’s watts per metre and you have watts per square metre — no area term, no width term.
W/m² from pitch alone
14.4 W/m strip
Watts per square metre by strip pitch
Target 30–50 W/m² for a printed face seen at normal distance, 50–80 for a bright retail face, and only go above 80 when the box is deep enough to spread it.
Rows for a face, at 200 mm pitch
| Face height | Rows | Metres (3 m wide) | Watts and density |
|---|---|---|---|
| 0.5 m | 3 rows | 9 m | 130 W · 86 W/m² |
| 1.0 m | 6 rows | 18 m | 259 W · 86 W/m² |
| 1.5 m | 8 rows | 24 m | 346 W · 77 W/m² |
| 2.0 m | 11 rows | 33 m | 475 W · 79 W/m² |
| 3.0 m | 16 rows | 48 m | 691 W · 77 W/m² |
Counted with a row at each edge, which is why the density creeps above the pure 72 W/m² on small faces — the extra row matters more when the face is short.
Choosing the pitch
Pitch is set by what sits between the strip and the eye. A 200 mm pitch behind a properly diffused face reads even; the same pitch behind a thin clear sheet with a 30 mm gap reads as stripes. Depth matters too: more air between strip and face means the bands blur out and you can open the pitch up, which is one reason a deeper profile is worth its freight.
The practical route is to fix the density first — decide 40 W/m² — then let pitch follow from the strip you have, then lay the rows out and see whether the count is sane. If it comes out at 17 rows on a 3 m face, either the strip is too weak for the pitch you wanted or the face wants a deeper box.
Where the count goes wrong
Counting rows, ordering metres. A 2 m × 3 m face at 200 mm pitch is 11 rows × 3 m = 33 m of strip, not 2 m × 3 m of area.
Forgetting the return. A wrapped face, or a box with a lit back panel, needs an extra run along the return — and that one is as long as the face is wide.
Double-sided boxes. Two faces need two sets of rows, not one set shared between them, unless the divider carries a reflector and the density was sized for it.
Frequently Asked Questions
Does a double-sided lightbox need double the strip?
Usually not double — a little more than single, because two faces share the same cavity and the light bounces. In practice most double-sided boxes run the same rows and add a reflector on the divider; check the density once both faces are lit.
Which way should the rows run?
Along the long side, so each row is as long as possible and the end losses are spread over fewer runs. On a tall narrow face that means horizontal rows; on a wide low one, the same rule still applies if you can fit the runs.
Can I mix pitches on one face?
You can, and on an L-shaped or a very tall face you sometimes have to, but keep the change at a rail or a corner. A pitch change in the middle of a flat face shows as a band.
Send the face size and the depth you have — we will return a row layout with metres, watts and the driver split. See our lightbox LED strip.
Products referenced
edge-lit and backlit LED strip, 12/24 V · SEG profiles with LED channels