Downlight sizes: cut-out diameter, depth, spacing and how many you need

Short answer: The most common downlight cut-out diameters are 55, 65, 75, 85, 95, 105 and 150 mm; the exact size is listed on each product page as the mounting (cut-out) dimension. A plasterboard ceiling needs a void at least 1–2 cm deeper than the fitting. In living rooms and bedrooms, downlights are usually spaced 1–1.5 m apart and 40–60 cm from the wall. A 20 m² living room needs roughly 8 downlights of 7 W (about 600 lm).

Cut-out sizes

• 55–65 mm: small accent lights and GU10 holders.
• 75–95 mm: the most common residential COB downlights (5–12 W).
• 105–150 mm: wide-beam downlights for shops and offices.
• 200 mm and up: large downlights for high ceilings and commercial spaces.

Check the cut-out and body height before drilling. A hole only a few millimetres too large leaves the springs nothing to grip; too small and the fitting will not go in. Square downlights need a square cut-out.

Ceiling void and heat

The body and driver sit inside the ceiling. Add 1–2 cm to the body height; if the driver is separate, place it beside the fitting in free air, not on top of insulation. Heat decides LED life: a downlight buried in mineral wool or foam runs hot and fails early.

Spacing and distance from walls

• Between lights: in homes with 2.6–2.8 m ceilings, usually 1–1.5 m. Wide beams (60° and up) allow wider spacing, narrow beams (24–36°) need closer spacing.
• From walls: 40–60 cm. To wash a wall (curtains, art, textured walls) use 30–40 cm and adjustable downlights; lights too close to the wall cast sharp scallops.
• Layout: arrange downlights around seating and work areas rather than in a single line down the middle, and do not drill until the furniture plan is fixed.

How many downlights?

Simple calculation: required lumens ≈ area (m²) × target lux ÷ 0.6.

• Living room and bedroom: 100–150 lux. 20 m² × 150 ÷ 0.6 ≈ 5,000 lm → 8 downlights of 600 lm.
• Kitchen worktop and work areas: 300–500 lux.
• Hallway: 100 lux; a single row 1.2–1.5 m apart.
• Bathroom: around 200 lux, with IP44 or higher downlights in wet areas.

Layering downlights with cove lighting and floor lamps is more comfortable than downlights alone; dimmable downlights let you lower the light in the evening.

Beam angle and colour

• 24–36°: accents, artwork, kitchen islands.
• 60°: the most common angle for general lighting.
• 90° and up: soft general light with low ceilings.
• Colour: 2700–3000 K at home, 3000–4000 K in kitchens and work areas; choose CRI 90 for true colours.
• Glare: deep-set downlights or honeycomb louvres avoid dazzle.

In Bursa, ENGN provides downlight layout plans, product selection and installation for homes and businesses.

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