A ceiling cove wants a mouth 150 to 200 mm (6 to 8 in) wide, a depth of at least 100 mm (4 in) above the strip, and the strip set 30 to 50 mm (1.2 to 2 in) back from the wall. Those are installation conventions, not standards.
What are the dimensions of a light cove?
A cove is sized by three dimensions: the width of its mouth from the wall face to the inner lip, the depth of the pocket from the top of the strip to the ceiling plane, and the height of the lip above the top of the strip. A working set for a residential ceiling is a mouth of 150 to 200 mm (6 to 8 in), a pocket depth of 100 to 150 mm (4 to 6 in), and a lip of 20 to 30 mm (0.8 to 1.2 in). A stepped perimeter ceiling follows the same logic at a smaller scale, with a return of 120 to 150 mm (4.7 to 5.9 in). The mouth decides how far the wash reaches across the ceiling, the depth decides whether the beam has room to spread before it lands, and the lip decides whether a standing eye sees the diodes. All three are fixed by the plasterer, so they belong on the section drawing.
| Dimension | Working range | What it decides |
|---|---|---|
| Mouth width, wall face to inner lip | 150 to 200 mm (6 to 8 in) | How far the wash travels across the ceiling |
| Pocket depth above the strip | 100 to 150 mm (4 to 6 in) | Whether the beam spreads before it lands |
| Lip above the top of the strip | 20 to 30 mm (0.8 to 1.2 in) | Whether a standing eye sees the diodes |
| Stepped perimeter return | 120 to 150 mm (4.7 to 5.9 in) | Whether the step reads as a detail or disappears |
| Strip set back from the wall face | 30 to 50 mm (1.2 to 2 in) | Whether the ceiling or the wall takes the light |
Why depth matters more than width
The mouth sets the reach of the wash and the depth sets its evenness, and of the two the depth is the harder one to correct after plastering. A strip is a line source that throws a cone, and a 24 V strip with a 120 degree beam needs roughly 100 mm (4 in) of travel before the cone has spread enough to land as a continuous band. At 50 mm (2 in) of depth the same strip lands as bright arcs of about 60 mm (2.4 in) where the pitch is coarser than 17 mm (0.7 in), which is what a 60 diodes per metre strip gives you. The effect is visible on smooth plaster from 2 m (6 ft 7 in) away, which is why a shallow cove looks expensive in a photo and cheap in a room. Depth also buys tolerance: a pocket of 150 mm (6 in) hides a channel, a driver and a diffuser, where 80 mm (3.1 in) hides the strip and little else.
Two checks settle the depth before the frame goes up. Confirm the driver can sit outside the pocket, in a cupboard or above a wardrobe, because a driver inside a closed cove runs hot and shortens its own life. Then confirm the ceiling plane is flat across the run: a 3 mm (0.12 in) dip over 3 m (9 ft 10 in) shows as a wave once the light grazes it, and skim coat is easier to correct before the pocket is built than after.
How much output does a cove need per metre?
Cove strip is specified in watts per metre, and the class is chosen by the surface it lights rather than by the floor area of the room. A 4.8 W/m (1.5 W/ft) strip suits a skirting, a step or a shelf, where the lit surface sits close enough that a low output still reads. A 9.6 W/m (2.9 W/ft) strip is the usual choice for a ceiling cove at 2.4 to 3 m (7 ft 10 in to 9 ft 10 in), because the light has to climb to the ceiling and then travel across it before it enters the room. A 14.4 W/m (4.4 W/ft) strip belongs above 3.5 m (11 ft 6 in), or in a cove with a pocket deeper than 200 mm (8 in), where the lit plane is large enough to absorb the extra output. The three classes are the same diode families run at 60, 120 and 180 diodes per metre.
| Strip class | Output | Where it belongs | What it is for |
|---|---|---|---|
| Light | 4.8 W/m (1.5 W/ft) | Skirting, step, shelf, wardrobe | Accent at close range |
| Standard | 9.6 W/m (2.9 W/ft) | Ceiling cove at 2.4 to 3 m (7 ft 10 in to 9 ft 10 in) | Ambient wash for the room |
| High | 14.4 W/m (4.4 W/ft) | Cove above 3.5 m (11 ft 6 in), pocket over 200 mm (8 in) | Ambient wash in a tall volume |
| Diffused | Same output, opal cover | Any cove with a visible lip | Removes the diode image, loses about 10 to 15 percent of output |
Twelve volts or twenty-four: where the run gets cut
Voltage decides how far one run travels before the far end dims, and the limit arrives sooner than most drawings assume. A 12 V strip at 4.8 W/m holds its output to roughly 5 m (16 ft) from the driver before the drop reads as a darker end; a 24 V strip of the same class reaches about 10 m (33 ft), and a 48 V strip about 20 m (66 ft). The figures move with copper weight and with the load, so a 9.6 W/m run is about half the length of a 4.8 W/m run at the same voltage, and a 5 m (16 ft) run of 12 V at 14.4 W/m will show a visible step at the far end. For a room with a 12 m (39 ft) perimeter that means two feeds rather than one continuous loop.
| Supply | Typical maximum run at 4.8 W/m | Typical maximum run at 9.6 W/m | What it costs you |
|---|---|---|---|
| 12 V | About 5 m (16 ft) | About 2.5 m (8 ft) | Short runs, more feeds, thicker cable |
| 24 V | About 10 m (33 ft) | About 5 m (16 ft) | The default for a residential ceiling |
| 48 V | About 20 m (66 ft) | About 10 m (33 ft) | Fewer feeds, driver is not a consumer unit item in every market |
One practical note belongs with the table: a driver sized exactly to the load will run near its limit, so leave headroom of about 20 percent on the driver rather than matching it to the strip. A 60 W driver on a 48 W run also leaves room for a second feed later, which is the cheaper way to fix a dark corner than opening the ceiling.
The cove and the chandelier on one ceiling
A cove and a central fixture share one ceiling, one switch plate and one impression, and the pairing only works when the two can be dimmed together. In our own catalogue at 16 October 2026 there were 1,381 products across 9,851 variants, and 818 of them stated 110 to 240 V, so supply voltage rarely rules a fixture out. Dimmability was declared on 37 products and smart control on 88, which is the line to check before ordering, because a cove on a dimmer and a chandelier on a plain switch give two fixed settings rather than a scene. Colour temperature was stated on 204 products and a colour rendering index on 176, and those two lines decide whether the indirect layer and the fixture agree when both are on.
| Line on the listing | Products stating it, 16 October 2026 | Why it matters next to a cove |
|---|---|---|
| Supply voltage | 818 of 1,381 state 110 to 240 V | Whether the fixture suits the market |
| Dimmable or dimming | 37, of which 36 state yes | Whether the two layers can be balanced at night |
| Smart control | 88 | Whether both can sit in one scene |
| Colour temperature | 204, of which 104 state 3000 K | Whether the fixture matches a 2700 to 3000 K cove |
| Colour rendering index | 176, of which 120 are RA80 and 52 in the 90 to 100 band | Whether crystals and plaster read true under both |
| Number of light sources | 241 | Whether the fixture gives points or a wash |
The ratio between the layers is the part that decides whether the combination reads as designed, and it is set out with numbers in how much light a dining table needs. Where the fixture has to hold its own against a lit ceiling, its size is the other half of the answer, and the width conversions are in chandelier sizes in inches and centimetres.
Colour temperature and rendering in an indirect layer
A cove stays on for long stretches and lights a large surface, so its colour temperature is more visible than the colour temperature of the fixture below it. Hold the cove at 2700 to 3000 K where the ceiling is white and the room is warm, because a cove at 4000 K reads as a lit office ceiling at night even when the chandelier over the table is 3000 K. Rendering matters for the same reason: the lit plane is what the eye compares everything else against. A strip at a colour rendering index of 90 or above holds white plaster and timber near their true colour, and a strip at 80 shows a grey cast across 12 m (39 ft) of ceiling that no amount of crystal in the room will hide.
Consistency along the run is the third line on the specification. Bins held within 3 SDCM, which is about 0.002 on the u-v plane, keep a long cove from reading as two colours where two reels were joined; the same tolerance is what keeps a multi-light chandelier from showing a mismatched lamp. Colour temperature bins follow the ANSI C78.377 quadrants, so a 3000 K strip from one supplier and a 3000 K fixture from another can still sit at opposite ends of the same bin, which is why the two are worth ordering against one target rather than against the label. Consistency between the layers matters more than the exact figure, and the fixture side of it is covered in chandelier colour temperature and dimming.
What to check before the plaster goes on
A cove is settled in five checks, and four of them happen before the plasterboard is closed, because a cove is a pocket built around a light source rather than a fitting hung on a ceiling. The sequence matters: the section drawing fixes the three dimensions, the standing test fixes the lip, the driver position fixes what can be serviced, and the feed points fix whether the far end of the run holds its output. The strip test at second fix is the one that still has a decision left in it, since the ceiling colour, the pocket depth and the diffuser all change the result by enough to see. Work through the five below in order, with the standing test taken at 2 m (6 ft 7 in), and note the finished wall face as the datum for every dimension, because a dimension taken from the stud moves once the plaster is on.
- Set the mouth and the pocket depth on a section drawing, and dimension both from the finished wall face rather than from the stud.
- Confirm the lip height at 20 to 30 mm (0.8 to 1.2 in) and stand 2 m (6 ft 7 in) back to test whether the diodes are visible from eye height.
- Mark the driver position outside the pocket, then mark the feed points at the lengths the voltage allows.
- Test one 2 m (6 ft 7 in) length of the chosen strip in the actual pocket before the second fix, with the ceiling painted, because plaster colour changes the result more than the strip does.
- Confirm the dimmer protocol matches both the strip driver and the fixture, since two protocols on one plate will not fade together.
The third item is the one that gets skipped, and it is the one that cannot be fixed later without cutting plaster. A cove with a feed at each end of a 12 m (39 ft) run costs two short cables; the same cove with one feed costs a repaint.
When a cove is not the right choice
An indirect cove is not the right choice where the ceiling is below 2.4 m (7 ft 10 in), because a pocket of 100 mm (4 in) plus a lip takes height the room does not have and the wash lands too close to the eye to read as soft. It is not recommended where the ceiling is the feature itself, such as a coffered or a moulded plaster ceiling, since the cove cuts across the detail it was meant to light. A cove is also the wrong answer when the complaint is a dark corner rather than a flat ceiling plane, because indirect light from the perimeter does not reach into a corner that faces away from it. Where the complaint is a pool of light landing in the wrong place rather than a lack of light at all, the fix is a cone width rather than another layer, and the geometry is worked through in downlight beam angle guide. And it is not the answer where the budget covers one lighting layer only: a single well-aimed fixture over the table does more for a dining room than a cove on its own, and the order of spending is set out in lighting schedule and rough-in before first fix.
Where the room already has a chandelier and needs more light, the cheaper sequence is usually to raise the output of the existing layer, or to add a floor or table lamp at the corner, before cutting a cove into a finished ceiling. Cove light is a design decision made at first fix, not a remedy applied afterwards.
Numbers and sources
The catalogue figures on this page are first-party and were recomputed mechanically from our own Shopify export of 16 October 2026: 1,381 products, 9,851 variants, 818 products stating 110 to 240 V, 204 stating a colour temperature with 104 of those stating 3000 K, 176 stating a colour rendering index with 120 at RA80 and 52 in the 90 to 100 band, 37 declaring dimmability with 36 stating yes, 88 stating smart control, and 241 stating a number of light sources. Each count comes from the specification lines inside the product descriptions rather than from a sample, so any of them can be checked against the listings. The cove dimensions, the strip output classes, the maximum run lengths and the 2700 to 3000 K band are installation and trade convention rather than standards, and no measurement of ours sits behind them.
| Figure | Value | Source | Nature |
|---|---|---|---|
| Catalogue size | 1,381 products / 9,851 variants | Shopify catalogue export, 16 October 2026 | First-party, recomputed |
| Supply voltage | 818 products state 110 to 240 V | Same export, specification lines | First-party, recomputed |
| Colour temperature | 204 products; 104 state 3000 K | Same export, specification lines | First-party, recomputed |
| Colour rendering index | 176 products; 120 RA80, 52 at 90 to 100 | Same export, specification lines | First-party, recomputed |
| Dimmable or dimming | 37 products; 36 yes, 1 no | Same export, specification lines | First-party, recomputed |
| Smart control | 88 products | Same export, specification lines | First-party, recomputed |
| Number of light sources | 241 products | Same export, specification lines | First-party, recomputed |
| Cove mouth width | 150 to 200 mm (6 to 8 in) | Installation convention | Not a standard, not measured here |
| Pocket depth | 100 to 150 mm (4 to 6 in) | Installation convention | Not a standard, not measured here |
| Lip above strip | 20 to 30 mm (0.8 to 1.2 in) | Installation convention | Not a standard, not measured here |
| Strip output classes | 4.8, 9.6 and 14.4 W/m | Trade convention, 24 V strip classes | Not a standard, not measured here |
| Maximum run | 5 m at 12 V, 10 m at 24 V, 20 m at 48 V | Trade convention for 4.8 W/m strip | Not a standard, depends on copper and load |
| Cove colour temperature | 2700 to 3000 K | Trade convention | Not a standard, not measured here |
| Colour consistency | 3 SDCM, about 0.002 on the u-v plane | Industry tolerance, ANSI C78.377 bins | Convention, not a measurement of ours |
No figure here promises a delivered light level, a delivered appearance or a position in search results. A cove is confirmed on site, with the ceiling painted, rather than from a drawing or a datasheet. Electrical work, including driver sizing, voltage drop and dimmer compatibility, belongs to a qualified electrician working to the code that applies on site.