A recessed linear light is a joint between two trades: the furniture factory cuts the groove, the lighting supplier fills it. This guide gives the dimensions we tool to, the tolerances that actually matter, and the order of operations that avoids rework.
The four dimensions that define the joint
Every recessed linear detail is fixed by four numbers: groove width, groove depth, flange or trimless, and cable exit. Get those on the drawing and the rest is standard.
| Detail | Groove width | Groove depth | Notes |
|---|---|---|---|
| 12 mm trim profile | 12.5 – 13 mm | 18 mm | Aluminium profile + opal diffuser, sits flush |
| 16 mm trim profile | 16.5 – 17 mm | 20 mm | Higher output, better heat spreading |
| 20 mm trimless | 20.5 mm + 2 mm rebate | 22 mm | Two-stage routing: rebate first, finish later |
| Wardrobe shelf light | 10 – 12 mm | 12 mm | Thin profile; driver must be remote |
Indicative tooling dimensions — confirm against the approved profile drawing before routing.
Width tolerance is ±0.3 mm on the groove and ±0.5 mm on position. Anything looser and the diffuser shows a shadow line along one edge, which is the first thing a hotel owner notices in a photograph.
Material behaviour you have to design around
MDF routes cleanly and holds ±0.2 mm, but the cut edge drinks moisture and swells under a hot profile. Seal it.
Plywood is more stable thermally but tears at the groove edge unless a down-cut bit is used.
Veneer and laminate must be applied after routing if the groove is trimless, otherwise the edge band lifts. This single sequencing decision is the most common cause of site rework.
Keep the profile at least 25 mm from any PU foam, and 15 mm from a raw MDF face that will not be sealed — LED profiles at 10 W/m reach 45–55 °C at the housing, which is enough to discolour a cheap laminate over a few thousand hours.
Thermal clearance and output
The profile is the heatsink. A 12 mm anodised aluminium profile can dissipate roughly 8–10 W/m before the LED junction temperature starts costing life; a 20 mm profile with fins handles 15–18 W/m. If you need more light than that in a 12 mm groove, the answer is a higher-efficiency LED, not more power.
Order of operations
- Approve the profile and the diffuser as physical samples on the actual veneer.
- Route a 300 mm test groove on an offcut; check the diffuser sits flush and the shadow line is even.
- Route production grooves; seal cut edges before finishing.
- Pull the cable through the 8 mm exit hole and leave a 300 mm service loop.
- Fit the profile and diffuser at the plant, not on site — this is what protects the finish.
- Test every fitting before packing; record the result against the room number.
Five faults we see repeatedly
| Symptom | Usual cause | Fix |
|---|---|---|
| Dark spot at the end of a run | LED pitch too wide at the end cap | Shorten the diffuser or specify a denser end section |
| Light visible from the side | Diffuser proud of the groove on one edge | Re-route with a 0.3 mm deeper groove, not a wider one |
| Shadow line along the wall | Groove not parallel to the wall face | Route from a reference face, not from the panel edge |
| Flicker when the wardrobe door closes | Driver shared with a sensor circuit | Separate driver per switched circuit |
| Yellowing diffuser after a year | PMMA instead of PC, or heat trapped by tape | Specify UV-stabilised PC and thermal tape |
Specifier's checklist
- Profile sample approved on the real veneer, in the real colour temperature
- Groove width, depth and position tolerances on the furniture drawing
- Cut edges sealed before finishing
- 25 mm clearance from foam, 15 mm from unsealed MDF
- Fittings assembled and tested at the plant, with per-room records
Questions we get asked
Can the diffuser be cut on site to fit?
What tolerance should the furniture factory hold on groove position?
Is trimless worth the extra cost?
How do I hide the cable?
Send the furniture drawing. We will answer with a lighting solution.
Cut-out drawings, photometric files and samples for the lines that fit your detail.
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