{
  "tool": "lighting",
  "version": "1.0.0",
  "inputs": {
    "room_length_cm": 450,
    "room_width_cm": 400,
    "ceiling_height_cm": 240,
    "room_type": "living",
    "wall_colour": "light"
  },
  "answer": {
    "total_lm": [
      3600,
      7200
    ],
    "target_lux": [
      100,
      200
    ],
    "task_lux": 200,
    "layers": {
      "ceiling": {
        "share_pct": 30,
        "light_lm": [
          1100,
          2150
        ]
      },
      "lamps": {
        "share_pct": 50,
        "light_lm": [
          1800,
          3600
        ]
      },
      "task": {
        "share_pct": 20,
        "light_lm": [
          700,
          1450
        ]
      }
    },
    "bulbs": [
      {
        "bulb_lm": 470,
        "count": [
          8,
          16
        ]
      },
      {
        "bulb_lm": 806,
        "count": [
          5,
          9
        ]
      },
      {
        "bulb_lm": 1055,
        "count": [
          4,
          7
        ]
      }
    ],
    "downlights": {
      "count": 12,
      "columns": 4,
      "rows": 3,
      "spacing_cm": [
        113,
        133
      ],
      "from_wall_cm": [
        56,
        67
      ],
      "each_lm": [
        92,
        179
      ]
    },
    "colour_temperature_k": [
      2700,
      3000
    ],
    "area_m2": 18,
    "room_index": 1.32,
    "utilisation": 0.5,
    "utilisation_light_walls": 0.5,
    "task_light": "reading lamps"
  },
  "summary": "A 4.5 m × 4 m living room needs 3,600–7,200 lumens from all its bulbs together, for 100–200 lux: about 30% from ceiling lights, 50% from lamps, 20% from reading lamps, at 2700–3000 K.",
  "working": [
    "Floor area = 4.5 × 4 = 18 m².",
    "Room index = 4.5 × 4 ÷ (1.6 × (4.5 + 4)) = 1.32, with 1.6 m from desk height to the ceiling.",
    "Utilisation factor = 0.3 + 0.15 × 1.32, kept between 0.35 and 0.65 = 0.5.",
    "Target 100–200 lux for a living room.",
    "Lumens = 100–200 × 18 ÷ 0.5 = 3,600–7,200 lm (rounded to 50).",
    "Downlights: 2.4 m × 0.5 = 1.2 m apart, so 4 × 3, 1.13 m × 1.33 m apart and 0.56 m × 0.67 m from the walls."
  ],
  "notes": [
    "These are targets for every light on at once. You will rarely run them all together, so fit dimmers."
  ],
  "sources": [
    {
      "label": "Spear Lighting, Technical section: residential lux levels from SLL LG9 (2013), BS EN 12464-1 and HSG38; office lux levels (catalogue pages 388–391, PDF of 18 Sep 2020)",
      "url": "https://static1.squarespace.com/static/601bc9c809d01b5ec47c23c6/t/604bb0611c93f475fa7675fc/1615573089670/Lighting+Guideline+Summary.pdf",
      "checked": "2026-10-31"
    },
    {
      "label": "CIBSE, SLL LG9 Lighting for communal residential buildings (2022 edition; paywalled, not read)",
      "url": "https://www.cibse.org/knowledge-research/knowledge-portal/lg9-lighting-for-communal-residential-buildings-2022",
      "checked": "2026-10-31"
    },
    {
      "label": "CIBSE Code for Interior Lighting (1994), hotel table as reproduced on SlideShare (bedroom 50–100, kitchen 150–300 lux)",
      "url": "https://www.slideshare.net/nosuhaila/led-lighting-code-for-interior-lighting-1994",
      "checked": "2026-10-31"
    },
    {
      "label": "electricaltechnology.org, Lighting design calculation in a building, step by step (lumen method; UF 0.66 at room index 1.8 with 70/50/20 reflectances)",
      "url": "https://www.electricaltechnology.org/2017/03/lighting-design-calculation-in-building.html",
      "checked": "2026-10-31"
    },
    {
      "label": "Emily Henderson, 19 lighting combos and rules (at least 2–3 light sources, at 2 or more heights)",
      "url": "https://stylebyemilyhenderson.com/19-lighting-combos-rules-lighting",
      "checked": "2026-10-15"
    },
    {
      "label": "Commission Regulation (EU) 2019/2020, equivalence claims for non-directional light sources (470 lm = 40 W, 806 lm = 60 W, 1055 lm = 75 W, 1521 lm = 100 W)",
      "url": "https://www.legislation.gov.uk/eur/2019/2020/pdfs/eur_20192020_2019-12-05_en.pdf",
      "checked": "2026-10-31"
    },
    {
      "label": "Philips Hue, How far should recessed lights be from the wall? (ceiling height ÷ 2 apart; 50–60 cm from the wall at 2.4 m)",
      "url": "https://www.philips-hue.com/en-us/explore-hue/faq/lamps/how-far-should-recessed-lights-be-from-the-wall",
      "checked": "2026-10-31"
    },
    {
      "label": "BLT Direct (7 May 2026), What is the difference between warm white, cool white and daylight LEDs?",
      "url": "https://www.bltdirect.com/what-is-the-difference-between-warm-white-cool-white-and-daylight-leds",
      "checked": "2026-10-31"
    }
  ],
  "page_url": "https://snuug.app/tools/lighting",
  "snuug": "Snuug is an iPhone app that rebuilds your room in 3D, to within about 3% of its real size, so you can redesign it and see what fits before you buy a thing. Not yet on the App Store (31 October 2026)."
}