{
  "id": "lumens",
  "version": "26c62562e3ff",
  "status": "published",
  "name": "Lumens Calculator",
  "question": "How many lumens do I need?",
  "summary": "Works out the lumens a room or work area needs from its size and a target light level in foot-candles or lux, and how many bulbs of a chosen brightness give it.",
  "category": "construction",
  "subcategory": "materials",
  "url": "https://www.acalculator.org/construction/lumens-calculator",
  "markdown": "https://www.acalculator.org/construction/lumens-calculator.md",
  "kind": "function",
  "method": "lumens = area × light level (ft² × foot-candles, or m² × lux); bulbs = lumens ÷ lumens per bulb, rounded up.",
  "assumptions": [
    "All the light from the bulbs reaches the work surface. Real rooms lose some to walls, shades and dirt, so a lighting designer adds more.",
    "The OSHA levels are legal minimums for construction sites and the offices on them, not comfort levels for a home.",
    "1 foot-candle = 1 lumen per square foot = 10.7639 lux (1 ft = 0.3048 m exactly)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "u": {
        "title": "Size in",
        "description": "Feet or meters for the room size.",
        "type": "string",
        "enum": [
          "ft",
          "m"
        ]
      },
      "l": {
        "title": "Length",
        "description": "The room or area length.",
        "type": "number",
        "minimum": 0.1,
        "maximum": 10000
      },
      "w": {
        "title": "Width",
        "description": "The room or area width.",
        "type": "number",
        "minimum": 0.1,
        "maximum": 10000
      },
      "t": {
        "title": "Light level",
        "description": "A minimum light level from OSHA’s table, or your own target.",
        "type": "string",
        "enum": [
          "custom",
          "office",
          "shop",
          "hall",
          "yard"
        ]
      },
      "lv": {
        "title": "Target light level",
        "description": "The light you want on the work surface, in the unit chosen next.",
        "type": "number",
        "minimum": 0.1,
        "maximum": 100000
      },
      "lu": {
        "title": "Light level in",
        "description": "Foot-candles (lumens per square foot) or lux (lumens per square meter).",
        "type": "string",
        "enum": [
          "fc",
          "lux"
        ]
      },
      "b": {
        "title": "Bulb brightness",
        "description": "The light output of each bulb, in lumens.",
        "type": "string",
        "enum": [
          "800",
          "450",
          "1100",
          "1600",
          "custom"
        ]
      },
      "pb": {
        "title": "Lumens per bulb",
        "description": "The lumens printed on the bulb’s package.",
        "type": "number",
        "minimum": 1,
        "maximum": 1000000
      }
    }
  },
  "outputs": {
    "lumens": {
      "label": "Lumens needed",
      "description": "Area × light level: foot-candles × square feet, or lux × square meters.",
      "format": "number"
    },
    "bulbs": {
      "label": "Bulbs",
      "description": "Lumens needed ÷ lumens per bulb, rounded up to a whole bulb.",
      "format": "integer"
    },
    "fc": {
      "label": "Light level (foot-candles)",
      "description": "The target in foot-candles (lumens per square foot).",
      "format": "number"
    },
    "lux": {
      "label": "Light level (lux)",
      "description": "The target in lux (lumens per square meter).",
      "format": "number"
    },
    "sqft": {
      "label": "Area (ft²)",
      "description": "Length × width in square feet.",
      "format": "number"
    },
    "sqm": {
      "label": "Area (m²)",
      "description": "Length × width in square meters.",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "u": "ft",
      "l": 12,
      "w": 12,
      "t": "office",
      "lv": 30,
      "lu": "fc",
      "b": "800",
      "pb": 800
    },
    "outputs": {
      "lumens": 4320,
      "bulbs": 6,
      "fc": 30,
      "lux": 322.9173125012917,
      "sqft": 144,
      "sqm": 13.37803776
    },
    "text": "You need about 4,320 lumens, or 6 bulbs."
  },
  "examples": [
    {
      "given": {
        "u": "ft",
        "l": 12,
        "w": 12,
        "t": "office",
        "b": "800"
      },
      "expect": {
        "lumens": 4320,
        "bulbs": 6,
        "fc": 30,
        "lux": 322.9173125012917,
        "sqft": 144
      },
      "source": "hand calculation in content.mdx: 144 ft² × 30 fc = 4,320 lm; 4,320 ÷ 800 = 5.4 → 6 bulbs; 30 ÷ 0.3048² = 322.917 lux; Python 3: Fraction; OSHA 29 CFR 1926.56, Illumination, Table D-3 (minimum foot-candles), https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56; NIST SP 811, Appendix B.9 (footcandle and lumen per square foot to lux: × 10.76391; 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9; US DOE FEMP, Purchasing Energy-Efficient Light Bulbs, Table 2 (450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W bulbs), https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs"
    },
    {
      "given": {
        "u": "m",
        "l": 4,
        "w": 3,
        "t": "custom",
        "lv": 300,
        "lu": "lux",
        "b": "1100"
      },
      "expect": {
        "lumens": 3600,
        "bulbs": 4,
        "sqm": 12,
        "fc": 27.870912
      },
      "source": "hand calculation in content.mdx: 12 m² × 300 lux = 3,600 lm; ÷ 1,100 = 3.27 → 4; 300 × 0.3048² = 27.870912 fc; NIST SP 811, Appendix B.9 (footcandle and lumen per square foot to lux: × 10.76391; 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9; US DOE FEMP, Purchasing Energy-Efficient Light Bulbs, Table 2 (450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W bulbs), https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs"
    },
    {
      "given": {
        "u": "ft",
        "l": 20,
        "w": 40,
        "t": "hall",
        "b": "custom",
        "pb": 1000
      },
      "expect": {
        "lumens": 4000,
        "bulbs": 4
      },
      "source": "hand calculation in content.mdx: 800 ft² × 5 fc = 4,000 lm; ÷ 1,000 = exactly 4 bulbs; OSHA 29 CFR 1926.56, Illumination, Table D-3 (minimum foot-candles), https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56"
    }
  ],
  "sources": [
    "OSHA, 29 CFR 1926.56 Illumination, Table D-3: minimum illumination intensities in foot-candles. https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.56 (retrieved 2026-10-19)",
    "NIST Special Publication 811, Appendix B.9: footcandle and lumen per square foot to lux, × 10.76391; 1 ft = 0.3048 m exactly. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9 (retrieved 2026-10-19)",
    "NIST Special Publication 811, Chapter 4, Table 3: the lux is one lumen per square meter. https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes (retrieved 2026-10-19)",
    "US Department of Energy, Federal Energy Management Program, Purchasing Energy-Efficient Light Bulbs, Table 2: 450, 800, 1,100 and 1,600 lumens for 40, 60, 75 and 100 W incandescent bulbs. https://www.energy.gov/cmei/femp/purchasing-energy-efficient-light-bulbs (retrieved 2026-10-19)"
  ],
  "related": [
    "square-footage",
    "wattage"
  ],
  "changelog": []
}