LED Aluminium Profile Sizes & PCB Width Matching: A Buyer's Guide
Most linear lighting problems are decided before anyone mounts a fitting. A profile is ordered against a sketch, the LED board is sourced separately, and the two meet on site: the strip will not seat in the channel, or the diffuser sits directly on the diodes. The fix is not a better installer — it is choosing the profile from the board, using the four measurements on every extrusion drawing. This guide sets out those measurements, the PCB channel widths behind the 186-section library, and a five-step selection method.
The board decides the profile, not the other way round
An aluminium profile is two products in one shape. The outside is a visible architectural envelope — how wide the line looks on the ceiling, whether it sits proud or recessed, whether it can be seen from below. The inside is a precision channel that holds a printed circuit board and a diffuser at fixed positions. Buyers who specify from the outside in tend to end up with a beautiful profile and a strip that does not belong in it.
The dependency is one-directional. Standard LED strip is manufactured in fixed PCB widths — 5, 8, 10, 12, 15, 20, 23, 26, 28, 31, 33, 37 and 47 mm are the bands we see most — and the PCB cannot be trimmed along its long edges without cutting the copper. So the strip arrives as a given, and the profile has to accommodate it.
The four measurements on any profile drawing
Ask for a dimensioned cross-section, not a photograph, and read these four numbers in order:
- Outer width × height (W × H) — the visible envelope, e.g. 20 × 20 mm. This decides how the line reads architecturally and whether it hides a driver.
- Inner PCB channel width — the slot the board sits in. This is the number that must match your strip, and it is always narrower than the outer width.
- Channel height (slot depth) — the clearance above the board. If this is too shallow, the diffuser presses on the LEDs and you get hot spots and uneven colour.
- Diffuser seat width and retention — how the PC cover is held (side grooves, snap-in lips or a flat seat). It determines whether the diffuser can be pre-fitted before shipping or must be fitted on site.
For runs above roughly 20 W per metre, add a fifth: wall thickness on the heat path. On a high-output line the extrusion is the heat sink, and thin decorative walls are the reason some 30 W/m installations discolour at the diffuser within a year.
PCB width to profile envelope: the matching table
The table below starts from the board and works outwards. It reflects the standard sections in our library; the die reference shown is only an example — on any given project the exact die number is what pins the tolerances.
| PCB width | Typical profile envelopes (W × H, mm) | Example dies | Where it is used |
|---|---|---|---|
| 5–6 mm | 8×7, 8×8, 8×9, 10×8, 10×10, 13×9 | TX-078, TX-079, TX-011, TX-012 | Cabinet, shelf and display strips; slim cove |
| 8 mm | 10×13, 11×7, 12×10, 12×12, 12×13, 15×9, 16×13 | XK-037B, TX-009, TX-010, XK-1210B | Thin display lines, tray and light-line detail |
| 10–12 mm | 13×7, 14×7, 14×8.8, 14.5×9, 15.5×6, 17×10, 17×12, 17.5×7, 21×9, 22×14.5, 24.5×7 | TX-133, TX-043, TX-128, TX-129, XK-142B, XK-143B | Office main lines and general linear runs |
| 15–17 mm | 19×13, 20×10, 20×12, 20×15, 20×20, 30×15, 30×20 | TX-038, TX-044, TX-041, TX-141, TX-018 | Suspended office pendants, mid-power runs |
| 18–20 mm | 20×10, 23×10, 23×20, 26×10, 29×29, 30×10 | TX-100, XK-101B, TX-031A, TX-136, TX-067 | Continuous office ceilings, medium output |
| 26–28 mm | 23×27, 30×10, 30×20, 30×30, 37×27 | XK-139B, TX-032, TX-040, TX-021 | High-output office lines, wide diffuser |
| 31–33 mm | 35×25, 35×35, 45×35 | TX-157, TX-023, TX-022 | Main-line architectural runs |
| 37 mm | 40×20, 55×20 | TX-001, TX-002 | Wide main-line, driver-in-profile |
| 45–47 mm | 50×20, 50×25, 65×20, 65×25 | TX-014, TX-016, TX-013, TX-015 | Seamless high-output main lines, 1:1 runs |
Two observations matter when you carry this table into a specification meeting. First, the same outer envelope can carry very different board widths: a 20 × 20 mm section appears in both the 15–17 mm and 18–20 mm bands because separate dies have different wall thicknesses. Second, at 45–47 mm the profiles stop being decorative trim and become structural — these are the dies used where a continuous line runs 10–15 m without a visible joint.
Special formats worth knowing about
Not every installation is a ceiling line, and the library carries sections for the awkward cases: in-ground dies for paving and façades (PCB channels of 23 mm and 45 mm), wood-clamping sections that grip an 18 mm board for joinery and reception desks, round sections at φ30 and φ60, triangular sections for corner mounting, and double-emission dies that light up and down from one line. All follow the same rule: channel width first.
A five-step selection method
- Fix the board. Decide PCB width and wattage per metre before anything else. If the board is not yet chosen, choose the strip and its power density now — it constrains everything downstream.
- Convert wattage into a heat path. As a working rule: up to about 10 W/m, the 8–12 mm sections are comfortable; 15–25 W/m wants a 20 × 20 mm or 30 × 20 mm section; above roughly 35–40 W/m you are in the 47 mm main-line dies, where the extrusion itself is the heat sink.
- Match the channel, with clearance. The PCB should sit 1–2 mm narrower than the internal channel. If your board is 10 mm, you are looking for a 12 mm channel, not a 12 mm profile.
- Choose the light direction. Downward only, double-up, double-down, or angled. This changes the diffuser seat and therefore the section, even at the same outer size.
- Close the accessories. Diffuser finish (opal, milky or clear), end caps, and corner connectors — 90° left and right, 135° and 180° — for the dies that accept them. Leaving connectors to the installer is how a clean line becomes a mitred joint filled with sealant.
Four mistakes that cost money on site
- Specifying the profile before the board. The most common cause of re-orders: the strip is fixed, the profile is the variable.
- Confusing outer width with channel width. A 20 × 20 mm section may take only a 17 mm board.
- Ignoring channel depth. A shallow slot puts the diffuser on the diodes — dotting, colour shift and premature yellowing of the PC cover.
- Forgetting connectors and end caps. Small line items on a quotation, large labour items on site.
What to put on your drawing
If you send one page, make it carry six items and the quotation will come back right the first time: (1) PCB width and strip wattage per metre; (2) run lengths, and whether joints are acceptable; (3) outer W × H if the envelope is fixed; (4) required internal channel width; (5) diffuser finish and whether it must be pre-fitted; (6) accessories — end caps and connector angles. Add the finish and any destination standard.
Frequently asked questions
What size aluminium profile do I need for a 10 mm LED strip?
Work from the channel, not the outer envelope. A 10 mm strip needs an internal PCB channel of at least 12 mm, which typically lands on a 14 × 7 mm, 15 × 9 mm, 17 × 10 mm or 17 × 12 mm section. A profile whose outer width is 12 mm will not take a 10 mm board once the diffuser seat is counted.
Can I fit a wider PCB into a narrower profile?
No. The PCB sits in a channel with a diffuser seat above it, so the board must be roughly 1–2 mm narrower than the channel for clearance. If the board does not fit, the profile changes — the strip cannot be trimmed along its edges without cutting the copper traces.
How many profile cross-sections are available?
The standard library covers 186 cross-sections from an 8 × 9 mm cabinet strip to a 65 × 25 mm main-line profile, with matched PCB channel widths from 5 mm to 47 mm. Each section is supplied as aluminium extrusion plus PC diffuser plus end caps, cut to the buyer's run lengths, with CRI 80–90 boards available in 3000 K, 4000 K and 6000 K where a fitted LED line is required.
Do you cut profiles to length and pre-fit the diffuser?
Yes. Profiles are cut to your run lengths before packing, and the diffuser and end caps can be pre-fitted so the sections arrive ready to install. Corner connectors — 90° left and right, 135° and 180° — are quoted per piece with the profile for the dies that accept them.
Send us the board, not the picture
Send the PCB width, the wattage per metre and the run lengths — or a section drawing if the envelope is fixed — and we will come back with the matching dies, a diffuser recommendation and the corner accessory list. It is a short email that prevents the re-order which costs a programme its schedule. See the full range on our linear aluminium profiles page, or the finished office line on our Glory linear light page (6063 aluminium body, UGR≤16/19/20 optics, 40/60/80 W).
Related reading: magnetic track specification — 48 V, 22 × 25 mm, die-cast vs extruded aluminium housings, and what to send for an accurate lighting housing quotation.