Work out your downlight layout
Positions are checked against the spacing-to-height ratio, so the light stays even.
How this calculator works
- Lumens required = target lux × area in m² ÷ (UF × 0.80). Same lumen method as the room lighting calculator, with the maintenance factor fixed at 0.80 for a normal flat.
- Minimum fittings = ceiling of (lumens ÷ fitting output). A 9 W downlight is taken as 900 lm, a 12 W as 1,200 lm.
- Grid columns = round(√(fittings × length ÷ width)), which produces the most square arrangement for the room's proportions. Rows are then the fittings divided by columns, rounded up.
- Spacing = length ÷ columns and width ÷ rows. The edge offset is half the spacing in each direction.
- Mounting height above the work plane = ceiling height − 2.5 ft, taking the working plane at table height.
- Evenness check: spacing must not exceed 1.2 × that mounting height in either direction. If it does, the calculator tells you to add a fitting or drop to a lower-output lamp.
| Downlight | Output | Covers at 150 lux | Typical use |
|---|---|---|---|
| 5 W | 450 lm | 14 sq ft | Accent, niche washing, wardrobe interiors |
| 7 W | 650 lm | 20 sq ft | Bedrooms and passages — the most forgiving size |
| 9 W | 900 lm | 28 sq ft | Living rooms; the default for a 9–10 ft ceiling |
| 12 W | 1,200 lm | 37 sq ft | Kitchens and higher ceilings |
| 15 W | 1,500 lm | 46 sq ft | Double-height spaces and stairwells only |
Coverage figures assume UF 0.60 and MF 0.80. Halve them for a 300 lux kitchen target.
Design and build under one accountable roof
Worked example: a 12 × 10 ft living room, 9 ft 6 in ceiling
- Area = 120 sq ft = 11.15 m²; target 150 lux; UF 0.60 × MF 0.80 = 0.48
- Lumens = 150 × 11.15 ÷ 0.48 = 3,484 lumens
- Fittings = 3,484 ÷ 900 = 3.87, rounded up = 4 downlights
- Columns = round(√(4 × 12 ÷ 10)) = round(2.19) = 2; rows = 4 ÷ 2 = 2
- Spacing = 12 ÷ 2 = 6.0 ft along the length, 10 ÷ 2 = 5.0 ft across; edge offset 3.0 ft and 2.5 ft
- Mounting height above the work plane = 9.5 − 2.5 = 7.0 ft; maximum even spacing = 1.2 × 7.0 = 8.4 ft
- 6.0 and 5.0 are both under 8.4, so the layout passes the evenness check. Connected load ≈ 36 W.
Placement rules a spacing grid will not give you
- Never centre a downlight on the room. A single fitting in the middle of a ceiling is the least useful position in the room. Grid from the edges inward.
- Keep downlights 2 to 2 ft 6 in off the wall where you want a wall wash, and use an adjustable or eyeball fitting. Any further out and you light the floor instead of the wall.
- Line up with the joinery, not the room. A downlight grid that ignores where the wardrobe front sits will put a fitting half-buried behind the cornice.
- Avoid downlights directly above a seated head in dining and living — the shadow falls exactly where you do not want it. Put light on the table, not on the crown of the head.
- Cut-out size and ceiling void. Confirm the fitting's cut-out diameter and the depth it needs above the board. A 12 W downlight typically wants 75 mm of void, which a 5 in ceiling drop does not always give once the duct is in.
- Circuit the perimeter separately. Perimeter downlights and cove lighting on one switch, central fittings on another, gives you two moods from the same install at no extra cost.
What this calculator does not cover
- Beam angle and glare control, which decide whether the room feels calm or clinical
- Adjustable, wall-wash and gimbal fittings, which are placed by intent rather than by grid
- Track, cove, profile and pendant lighting layers
- Driver location, dimming protocol and switching circuits
- The fitting and wiring cost — the false ceiling calculator includes downlights at ₹650 each fitted
This calculator uses the same rate bands and site rules our estimators apply, taken from Greenbox project records and cross-checked against 2026 supplier and contractor quotations in Mumbai. It is an indicative estimate, not a quotation — the real figure depends on your drawings, site condition and the brands you finally specify.
Grid versus layered: when the calculator is the wrong tool
An even downlight grid is the right answer for a kitchen, a passage, a utility area and a home office — spaces where you want uniform, shadow-free light on a work plane and nobody is going to sit and look at the ceiling. It is the wrong answer for a living room or a bedroom, where an even grid produces the flat, shadowless look people describe as feeling like an office.
In those rooms, use the count this calculator gives you as a total lumen budget and spend it differently: a perimeter cove carrying half of it, three or four adjustable downlights washing the joinery and artwork, and a floor or table lamp carrying the rest. The lux target is met, the wattage is the same, and the room reads completely differently.
Setting the grid out on site
- Chalk it before you cutSnap the grid onto the boarded ceiling with a chalk line, with the joinery already marked on the floor below. Stand in the room and look up before a single hole is cut.
- Check against the beamsConcealed beams and the AC duct run inside the ceiling void. A cut-out that lands on a beam moves — and once it moves, the whole row looks wrong unless you shift it as a set.
- Confirm cut-out diameterHave the actual fitting in hand. Cut-out diameters vary by several millimetres between brands, and a hole cut oversized cannot be made good invisibly.
- Leave driver accessEvery downlight has a driver sitting in the void. Where the ceiling is fully sealed, group drivers near an access panel or a grille so a failed driver does not mean cutting the ceiling.
Selected work by Greenbox Design Studio. Tap any image to enlarge.
Frequently asked questions
How many downlights do I need for a 12 × 10 room?+
Four 9 W downlights at 900 lumens each, in a 2 × 2 grid spaced 6 ft by 5 ft with a 3 ft and 2.5 ft edge offset, for a 150 lux living-room target. For a kitchen at 300 lux the same room needs eight, or five 12 W fittings.
What is the right spacing between downlights?+
No more than 1.2 times the mounting height above the working plane. With a 9 ft 6 in ceiling, that is a mounting height of 7 ft and a maximum spacing of about 8 ft 6 in. Edge fittings go at half the spacing from the wall, not the full spacing.
Is it better to have more small downlights or fewer bright ones?+
More small ones. Six 7 W fittings produce a far more even wash than three 15 W, and the individual glare is lower. Bright fittings spaced widely create scallops on the floor and hot spots on the ceiling plane between them.
How far should a downlight be from the wall?+
Two to two and a half feet if you want a wall wash, using an adjustable or eyeball fitting aimed at the wall. For general lighting, the edge offset from the grid — half the spacing — is the right answer, which in most rooms lands between 2 and 3 feet.
Can I change the downlight positions later?+
Only by cutting the ceiling open, patching, re-puttying and repainting the whole plane, because a patch never takes paint identically. Set the grid out on the boarded ceiling with a chalk line and stand in the room before anything is cut.