Lumen Method Calculator

Lumen Method Formula

Worked Example

A 10 × 8 m office lit to 300 lux with twin 3000 lm luminaires, UF 0.6 and MF 0.8:

1. N = E A / (F n UF MF) = 300 × 80 ÷ (3000 × 2 × 0.6 × 0.8) = 8.333333333

Illuminance achieved with that number: 324 lux · Room index K = LW/(Hm(L + W)): 2.02020202

GATE tip

Round up to a number that fits a regular grid, then recheck the spacing-to-mounting-height ratio of the luminaire.

More Building Physics and Services Calculators

• Reverberation Time Calculator

  T₆₀ = 0.161 V / ΣSα

  Eyring: T = 0.161 V / (−S ln(1 − ᾱ))

  Example: A 1000 m³ hall with 200, 200 and 300 m² of surfaces at α = 0.02, 0.3 and 0.1: Reverberation time (Sabine) T₆₀ = 1.71277 s.

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• Air Changes per Hour Calculator

  Q = ACH × V

  Q in m³/h, V room volume in m³

  Example: A 6 × 5 × 3 m room at 6 air changes per hour: Airflow = 540 m³/h.

  Open the air changes per hour calculator →

• Solar Angle Calculator

  sin α = sin φ sin δ + cos φ cos δ cos h

  δ = 23.45 sin(360(284 + n)/365); h = 15° × (t − 12)

  Example: Latitude 23° N at solar noon on 21 June: Solar altitude α = 89.5502 °.

  Open the solar angle calculator →

• U-Value Calculator

  U = 1 / (R_si + Σ d/λ + R_so)

  R_si = 0.13, R_so = 0.04 m²·K/W for walls (ISO 6946)

  Example: A 230 mm brick wall plastered 20 mm on both faces: U-value = 1.96268 W/(m²·K).

  Open the u-value calculator →

Frequently asked questions

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.