Lighting Calculator

Calculate how many light fixtures are needed to properly illuminate a room based on foot-candle requirements.

Results

Visualization

How It Works

Proper lighting is measured in foot-candles (lumens per square foot). Different rooms need different light levels: a kitchen or office needs about 50 foot-candles for detailed work, while a bedroom only needs about 20 foot-candles for comfortable ambient light.

The Formula

Lumens Needed = Room Area (sq ft) x Foot-Candles. Fixtures = Lumens Needed / Lumens Per Fixture.

Variables

  • Foot-candle — One lumen per square foot -- the standard unit of illumination
  • Lumen — The total light output of a bulb or fixture
  • Watt — Energy consumed by the fixture (lower for LED vs incandescent at same lumens)
  • Efficacy — Lumens per watt -- LED bulbs achieve 80-100+ lm/W vs 15 lm/W for incandescent

Example

A 15 x 12 ft office (180 sq ft) needs 50 foot-candles: 180 x 50 = 9,000 lumens. With 800 lumen LED bulbs: 9,000 / 800 = 12 fixtures (or four 3-bulb fixtures).

Tips

  • Layer your lighting: combine ambient (overhead), task (desk lamp), and accent (wall) lighting for the best results.
  • LED bulbs produce about 80-100 lumens per watt. An old 60W incandescent equals an 8-10W LED.
  • Spacing recessed lights: divide ceiling height by 2 for the maximum distance between cans (8 ft ceiling = 4 ft spacing).
  • Light color temperature matters: 2700K (warm) for living spaces, 4000K (neutral) for kitchens, 5000K (daylight) for workshops.
  • Dimmer switches give you flexibility -- use them with dimmable LED bulbs for energy savings and mood control.