Choosing a wide cob led strip or a narrow one is framed as a question about the groove, which is why so many strips are ordered at a width that fits the drawing but not the finished detail. Width is a dimension on a datasheet; clearance is what the installation needs, and the two are never the same number.
This guide sets out what strip width really controls — copper cross-section, thermal path, solder-pad size and achievable run length — so specifiers selecting COB LED Strip for joinery, handrails, coves and retail shelving can size a circuit against the profile rather than the catalogue.
What Strip Width Actually Controls
Width is treated as a fitment property. It is really an electrical and thermal one, and three consequences follow from the same millimetres.
Copper cross-section. The conductor carrying current is a copper trace, and its cross-section is width times copper thickness. A 10 mm circuit carries proportionally more copper than an 8 mm one at the same copper weight, so it drops less voltage per metre at the same load — the mechanism behind almost every long-run difference between otherwise identical builds.
Thermal path. COB emits along a continuous line rather than at discrete points, so heat is produced continuously and must leave through the circuit into whatever it is bonded to. A wider circuit presents more area to the profile floor, so a narrow strip at the same W/m runs hotter in the same extrusion.
Solder-pad area. Pads scale with width. On a narrow build the pad is small and the copper around it thin, so a soldering iron’s heat reaches the adjacent LEDs faster — a field-reliability issue rather than a manufacturing one, since the joints that fail are usually those made on site.
So a wide cob led strip is not a brightness setting and not merely a fitment choice. Width sets how far a run can go, how hot it gets, and how forgiving it is of on-site termination.
Two things it does not set cause frequent errors. Width is not brightness — output comes from watts per metre and efficacy, so a narrow strip at 14 W/m emits more than a wide one at 8 W/m. Width is not the dot-free surface either: continuity depends on diffuser depth being at least equal to LED pitch, and COB pitch satisfies this at 5 mm as readily as at 12 mm. What breaks continuity is a shallow diffuser or a strip mounted too close to it — the dotless cob led strip guide covers how pitch, diffuser depth and viewing distance interact.
Width does have one real visual effect: it sets how broad the emitting line is, so a 10 mm strip behind a wide diffuser gives a thicker band of light than a 5 mm strip. Decide that from a mock-up.
The Clearance Arithmetic Nobody Does Before Ordering
An 8 mm strip does not fit an 8 mm channel. This is the most common width failure, and it is arithmetic, not judgement.
Between nominal strip width and nominal channel width sit four tolerances, all consuming clearance in the same direction:
- Circuit tolerance. A nominal 8 mm circuit is cut to a tolerance, so a reel may run over.
- Adhesive thickness. The tape adds height, and where it squeezes out under pressure it adds edge width.
- Extrusion draft and radius. An extruded channel is not a true rectangle — walls carry a draft and corners a radius, so usable width at the floor is less than the quoted dimension.
- Coating, where present. Any conformal or silicone layer adds to both.
Allow roughly 1 mm over nominal width: an 8 mm strip wants about 9 mm of internal channel, a 10 mm strip about 11 mm. Forcing a strip into an exact-width channel produces failures that look like product defects but are not — it buckles rather than lying flat and loses thermal contact, the edges lift so the bond is only partial, and a strip pushed in cannot be pulled out for service without damage.
Two further dimensions come off the profile drawing, not the product page: internal depth rather than external height — a profile quoted as 12 mm tall may offer 7 mm inside once base thickness and diffuser seat are subtracted — and depth below the diffuser, which sits partway up the wall and consumes part of the cavity.
Width Map From 5 mm to 12 mm
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The table gives the channel each width needs and the constraint that rules it out. Our standard builds run 8 mm, 10 mm and 12 mm; narrower circuits are a different construction class, covered next.
| Nominal width | Internal channel needed | Where it is the right answer | The constraint that rules it out |
|---|---|---|---|
| 3 mm to 5 mm | About 4 mm to 6 mm | Shadow gaps and reveals too shallow for a standard circuit | Minimal copper, small pads; short reach before drop forces another feed |
| 8 mm | About 9 mm | Joinery grooves, shelving, display detail, cabinet work | Copper cross-section limits the length reachable at higher W/m |
| 10 mm | About 11 mm | Cove, corridor and long architectural runs | Will not enter a groove machined for 8 mm |
| 12 mm | About 13 mm | Multi-channel builds — RGBW, RGBCW, addressable | Channel count sets the width, so it cannot be traded for space |
Read the last column first. Width is chosen by eliminating what a project cannot tolerate, not by picking whichever sounds most capable — and on a multi-channel build it is no choice at all, because four channels of conductor have to fit somewhere.
What a Narrow Build Costs You
Narrow circuits exist because some details cannot take a standard strip — a shadow gap in a plasterboard reveal, a slot in a thin shelf edge, a rebate in a slim handrail. Where the detail is fixed and shallow, a narrow build is correct, but it is a trade, not a free reduction.
Reach falls with copper. Halving the width roughly halves the copper cross-section and doubles resistance per metre. Against the usual 10% drop limit, a narrow build reaches materially less length from one feed at the same W/m — forcing additional injection points, each a cable route and a termination the joinery has to accommodate.
Heat concentrates. Less area against the profile floor means a higher junction temperature at equal W/m, and junction temperature governs lumen maintenance over service life. So specify a narrow build at lower W/m in the same profile: the way to use a narrow strip successfully is to ask less of it.
Termination gets harder. Small pads and thin adjacent copper make field soldering less forgiving, and a shallow detail often has no room to dress the joint or provide strain relief. Where a narrow strip is unavoidable, specify pre-terminated lengths cut to the drawing so joints are made in a factory, not inside a cabinet.
The rule is straightforward: if the detail can be redesigned to take a standard width, redesign the detail. Widening a groove by 2 mm is cheap at the joinery stage and impossible after installation.
Width, Run Length and Voltage Are One Decision
Width is usually settled by the joinery and voltage later by the electrician, which is how projects arrive at a circuit that fits the groove but cannot reach the end of it. These are one calculation.
Voltage drop depends on current, and current at a given power is inversely proportional to voltage. A 10 W/m load draws about 0.83 A/m at 12V and about 0.42 A/m at 24V — half the current for the same light, so roughly half the drop per metre. Doubling the voltage buys more reach than widening the strip does.
That gives an order of operations when a run will not reach.
- Move to 24V if the cut interval allows. This gains the most reach and costs nothing in the groove. It is unavailable only when the detail needs short modules, since the 24V cut unit is longer.
- Widen the strip if the channel allows. Going from 8 mm to 10 mm adds copper and reach, but only if the groove is not already machined.
- Ask for heavier copper at the same width. Copper weight is specified in ounces per square foot, and a 2 oz circuit has roughly twice the conductor of a 1 oz one at identical outside dimensions. It costs no space, and it is the option buyers most often do not know to ask for.
- Feed both ends. This roughly quarters the worst-case drop of a single-end feed, since each half carries half the length.
Size the driver at about 80% of rating: a 14 W/m strip over 15 m draws 210 W and wants a 260 W supply. Where a detail forces short modules and rules out step one, how to cut cob led strip covers why cut intervals differ between voltages. Protective separation on the low-voltage side follows the IEC 61140 protection against electric shock standard, the framework these SELV circuits are built to.
Matched Width Options
Two 8 mm builds cover most standard-width work, separated by density and voltage.
COB 320 LEDs/m 8 mm is the lower-density build, at 12V and 24V. Use it at 12V where the detail needs short modules — shelf undersides, display niches, handrail sections — since the 12V cut unit is the shorter of the two and wastes less against a fixed dimension. At 24V it serves the same grooves over longer runs.
COB 480 LEDs/m 8 mm 24V is the higher-density build for the same channel width: grooves already machined at 8 mm where more output is wanted and the run is long enough for 24V to be the sensible bus. Both fit the same profile, so choosing between them is about output and run length, not fitment.
For a wider circuit, a 10 mm single-colour build carries more copper in a groove machined at 11 mm, and 12 mm builds exist because multi-channel constructions require the width. All are IP20 at CRI 90. Where a run meets moisture, the ingress classes in IEC 60529 describe a sealed assembly with different outside dimensions — dimension it into the channel from the start, not as the same strip with a coating.
Settle colour temperature in the same sample round as width, since profile depth and diffuser material both shift the apparent tone. The warm white cob led strip guide covers what a CCT figure does and does not commit a supplier to.
How Width Decides Differently in Three Installations
The same width question resolves differently depending on what is already fixed when the lighting is specified.
Cabinets and shelving
The groove is machined before the strip is ordered, so width is constrained and only density and voltage remain open. Runs are short, so drop is rarely the limit; the real constraints are cut interval against a fixed carcase dimension and whether the strip can be replaced without dismantling the unit. Standard 8 mm at 12V usually resolves both, as in this cabinet cob led strip lighting project.
Narrow joinery details
Where the detail is a shadow gap or slim reveal that cannot be widened, width is the fixed input and everything else adapts: lower W/m for the smaller thermal path, shorter runs per feed, and pre-terminated lengths, since soldering into a narrow rebate on site is unreliable. This cabinet joinery narrow COB LED strip lighting project shows the approach where the architecture will not move.
Handrails and stairs
The distinguishing constraint is the bend. Flexible circuits bend freely on one axis and not at all on the other, so a raked handrail must be planned with the required curvature in the bending plane. Width matters because a wider circuit resists bending more, and the rebate in a slim rail is both narrow and shallow. Service access matters too: a strip bonded inside a closed rail is permanent. This stair handrail COB LED strip lighting project shows how bending path and wire exits are set out.
In cove and corridor work the channel is specified with the lighting, so the wider build is generally correct: runs are long and the extra copper keeps the far end inside tolerance. The cob led strips for home decor guide covers how furniture and interior details are built.
Approving a Width So It Survives Installation
A loose sample on a desk confirms nothing about width, because every failure mode involves the channel. Approve it assembled.
- Fit the sample into the actual extrusion, not a numerically equivalent one. It should slide in and lie flat under light pressure; if it needs pushing, the clearance is wrong and it will not stay bonded. Check it comes out again too — anything that cannot be removed without damage is a permanent installation.
- Terminate it the way the site will. Make a sample joint at the intended width and confirm the channel has room to dress the cable and provide strain relief.
- Close the diffuser and check depth, not only width. A strip can fit side to side and still sit too close to the diffuser once the cover clips on.
- Run it to thermal equilibrium in the profile. Minutes on a bench prove nothing; what matters is the steady state in the actual extrusion and orientation, as an enclosed cabinet vents worse than an open cove.
- Measure the far-end voltage on a full-length run. Measure rather than calculate, and confirm it sits within 10% of nominal at the intended load.
- Bend it along the intended path. Confirm the curvature lies in the plane the circuit actually bends in and the radius is achievable at that width.
Lumen maintenance data reported to Illuminating Engineering Society LM-80 procedures is measured at defined case temperatures, so it predicts service life only if the installed thermal path resembles the tested one — which is why step five matters.
Common Questions on COB Strip Width
Is a wide COB LED strip brighter than a narrow one?
No. Output comes from watts per metre and efficacy, so a narrow strip at 14 W/m emits more than a wide one at 8 W/m. A wider circuit gives more copper and thermal contact area — longer reach from one feed and a lower junction temperature, not more lumens.
My run will not reach. Should I order a wider strip?
Try voltage first. The same load draws half the current at 24V as at 12V, so it drops roughly half the voltage per metre — a bigger gain than widening, at no cost in the groove. Then heavier copper at the same width, then feeding both ends, which roughly quarters the worst-case drop. Widening helps only if the channel is not yet machined.
Should width be chosen before or after the profile?
Together, and both before the joinery is cut. Take internal width and depth below the diffuser from the profile drawing, add the clearance allowance, then choose the strip. Where a detail is 2 mm too narrow for a standard build, widening the groove is far cheaper than accepting the compromises a narrow circuit brings.
Send Us the Profile Drawing
Width cannot be recommended from a room name. Send the profile’s internal width and depth below the diffuser, the longest continuous run and where power enters, the shortest module the detail requires, the bend radius and plane if the run curves, and the target output. Talk to our engineers and we will confirm the width, voltage and copper weight those constraints allow — and say where the groove, rather than the strip, needs to change.
