{
  "id": "recessed-lighting",
  "version": "0245b0f14e89",
  "status": "published",
  "name": "Recessed Lighting Calculator",
  "question": "How much recessed lighting do I need?",
  "summary": "Computes how many recessed (can) lights a rectangular room needs on an even grid, the spacing between them, the distance from the walls, and the lumens per square foot.",
  "category": "construction",
  "subcategory": "materials",
  "url": "https://www.acalculator.org/construction/recessed-lighting-calculator",
  "markdown": "https://www.acalculator.org/construction/recessed-lighting-calculator.md",
  "kind": "function",
  "method": "Spacing = ceiling height ÷ 2 (or the spacing you type); lights along each wall = wall length ÷ spacing, rounded up; lights = along × across; gap = wall length ÷ lights on it; distance from the wall = gap ÷ 2.",
  "assumptions": [
    "Lights at most half the ceiling height apart (Amico and Lumary: an 8 ft ceiling gives 4 ft).",
    "An even grid, with the outer lights half a gap from the walls (Amico).",
    "Brightness is the fixtures’ total lumens over the floor area; Lumary uses about 10 to 20 lumens per ft² for a living room or bedroom."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "l": {
        "title": "Room length",
        "description": "The length of the room, wall to wall.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.1,
        "maximum": 100
      },
      "w": {
        "title": "Room width",
        "description": "The width of the room, wall to wall.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.1,
        "maximum": 100
      },
      "h": {
        "title": "Ceiling height",
        "description": "The height of the ceiling above the floor.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.1,
        "maximum": 30
      },
      "s": {
        "title": "Spacing between lights",
        "description": "The largest gap you want between lights. Leave empty to use half the ceiling height.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.1,
        "maximum": 30
      },
      "lm": {
        "title": "Lumens per light",
        "description": "The light output of one fixture, in lumens, from its box. Leave empty to skip brightness.",
        "type": "number",
        "minimum": 1,
        "maximum": 100000
      }
    }
  },
  "outputs": {
    "count": {
      "label": "Lights",
      "description": "Lights along the length × lights along the width.",
      "format": "integer"
    },
    "along": {
      "label": "Lights along the length",
      "description": "Room length ÷ spacing, rounded up.",
      "format": "integer"
    },
    "across": {
      "label": "Lights along the width",
      "description": "Room width ÷ spacing, rounded up.",
      "format": "integer"
    },
    "gapL": {
      "label": "Gap along the length (ft)",
      "description": "Room length ÷ lights along the length, in feet.",
      "format": "number"
    },
    "gapW": {
      "label": "Gap along the width (ft)",
      "description": "Room width ÷ lights along the width, in feet.",
      "format": "number"
    },
    "wallL": {
      "label": "From the end walls (ft)",
      "description": "Half the gap along the length, in feet.",
      "format": "number"
    },
    "wallW": {
      "label": "From the side walls (ft)",
      "description": "Half the gap along the width, in feet.",
      "format": "number"
    },
    "gapLm": {
      "label": "Gap along the length (m)",
      "description": "The gap along the length in metres.",
      "format": "number"
    },
    "gapWm": {
      "label": "Gap along the width (m)",
      "description": "The gap along the width in metres.",
      "format": "number"
    },
    "perFt2": {
      "label": "Lumens per ft²",
      "description": "Lights × lumens per light ÷ the floor area in square feet.",
      "format": "number"
    },
    "total": {
      "label": "Total lumens",
      "description": "Lights × lumens per light.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "l": 4.572,
      "w": 3.6576000000000004,
      "h": 2.4384
    },
    "outputs": {
      "count": 12,
      "along": 4,
      "across": 3,
      "gapL": 3.75,
      "gapW": 4,
      "wallL": 1.875,
      "wallW": 2,
      "gapLm": 1.143,
      "gapWm": 1.2192
    },
    "text": "You need 12 recessed lights: 4 along the length and 3 along the width."
  },
  "examples": [
    {
      "given": {
        "l": 4.572,
        "w": 3.6576000000000004,
        "h": 2.4384
      },
      "expect": {
        "along": 4,
        "across": 3,
        "count": 12,
        "gapL": 3.75,
        "gapW": 4,
        "wallL": 1.875,
        "wallW": 2
      },
      "source": "Amico, Where to Place Recessed Lights (ceiling height ÷ 2; perimeter lights half the spacing from the walls), https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room; hand calculation in content.mdx: 15 ÷ 4 = 3.75 → 4, 12 ÷ 4 = 3, 4 × 3 = 12"
    },
    {
      "given": {
        "l": 6.096,
        "w": 4.2672,
        "h": 3.048,
        "lm": 800
      },
      "expect": {
        "along": 4,
        "across": 3,
        "count": 12,
        "gapW": 4.666666666666667,
        "total": 9600,
        "perFt2": 34.285714285714285
      },
      "source": "Lumary, What is the recommended spacing between each recessed light? (roughly half the ceiling height; a 10 ft ceiling about 5 ft apart), https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light; hand calculation in content.mdx: 12 × 800 = 9,600 lm ÷ 280 ft² = 34.3 lm/ft²"
    },
    {
      "given": {
        "l": 4,
        "w": 3,
        "h": 2.4
      },
      "expect": {
        "along": 4,
        "across": 3,
        "count": 12,
        "gapLm": 1,
        "gapWm": 1
      },
      "source": "Amico, Where to Place Recessed Lights (ceiling height ÷ 2), https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room; hand calculation in content.mdx: spacing 1.2 m; 4 ÷ 1.2 = 3.33 → 4; 3 ÷ 1.2 = 2.5 → 3"
    },
    {
      "given": {
        "l": 4.572,
        "w": 3.6576000000000004,
        "h": 2.4384,
        "s": 1.8288000000000002
      },
      "expect": {
        "along": 3,
        "across": 2,
        "count": 6,
        "gapL": 5,
        "gapW": 6
      },
      "source": "Lumary, recommended spacing between recessed lights (4 to 6 ft for typical downlights), https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light; hand calculation in content.mdx: 15 ÷ 6 = 2.5 → 3; 12 ÷ 6 = 2"
    }
  ],
  "sources": [
    "Amico, Where to Place Recessed Lights: The Rule of Thumb for Every Room (ceiling height ÷ 2: 8 ft ceiling 4 ft apart, 9 ft 4.5 ft, 10 ft 5 ft; perimeter fixtures half the spacing from the walls). https://amicolight.com/blogs/news/where-to-place-recessed-lights-the-rule-of-thumb-for-every-room (retrieved 2026-10-02)",
    "Lumary, What is the recommended spacing between each recessed light? (space each light at roughly half the ceiling height; 4–6 ft for typical downlights; 1,000–2,000 lumens for a 100 ft² living room or bedroom). https://www.lumarysmart.com/blogs/news-and-blogs/what-is-the-recommended-spacing-between-each-recessed-light (retrieved 2026-10-02)",
    "NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement: 1 ft = 0.3048 m; 1 ft = 12 in. https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-01)"
  ],
  "related": [
    "square-footage",
    "electricity-cost",
    "paint"
  ],
  "changelog": []
}