💡 Electrical

Lux Level Calculator

Calculate the number of luminaires needed to achieve required lux levels in any room. Uses lumen method per SP 72 and NBC 2016 lighting standards.

📐 Standard: SP 72 / NBC 2016 Part 8
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

The lux level calculator uses the lumen method to determine how many luminaires are required to achieve a specified illuminance (in lux) in a space. The method accounts for room geometry through the Room Cavity Ratio (RCR) and light losses through the Maintenance Factor (MF). Recommended lux levels for different tasks are specified in SP 72 (NBC Handbook) and NBC 2016 Part 8.

SP 72 (National Building Code Handbook on Lighting) provides recommended illuminance levels: office general – 300–500 lux; conference – 500 lux; manufacturing – 300–750 lux; hospital ward – 100 lux; ICU – 300 lux; classroom – 300–500 lux; parking – 50 lux. NBC 2016 Part 8 mandates minimum lux levels for different building types. Energy compliance: NBC 2016 limits Lighting Power Density (LPD) which must be checked alongside lux levels.

📐 Lumen Method Formula

SP 72 / NBC 2016 Part 8

RCR = 5 × H_c × (L + W) / (L × W)
Where: H_c = cavity height (ceiling to work plane, m), L = length, W = width

CU (Coefficient of Utilisation): from manufacturer table vs RCR, reflectances

N = (E × A) / (Φ × CU × MF)
Where:
  N = number of luminaires
  E = required illuminance (lux)
  A = room area (m²)
  Φ = lumens per luminaire
  CU = coefficient of utilisation (0.4–0.8 typical)
  MF = maintenance factor (0.7–0.8 typical)

❓ Frequently Asked Questions

What is a good maintenance factor (MF) to use? +
MF accounts for lamp lumen depreciation, luminaire dirt accumulation, and room surface dirt. Typical values: clean environment with LED (annual cleaning): MF = 0.80; office with quarterly cleaning: MF = 0.75; industrial with dust: MF = 0.65–0.70. LED luminaires have much less lumen depreciation than fluorescent, so their MF is higher. Always use manufacturer's LLF (Light Loss Factor) data when available.
What lux levels are required for offices? +
Per SP 72: open-plan office (general) = 300–500 lux; computer workstations = 300–500 lux (with glare control); meeting rooms = 300–500 lux; corridors = 100–200 lux; reception = 200–300 lux; filing areas = 200 lux. NBC 2016 mandates minimum 300 lux for normal office work. Higher lux (500+) improves productivity for detailed tasks.
How do I calculate Room Cavity Ratio (RCR)? +
RCR = 5 × Hc × (L + W) / (L × W), where Hc is the height from the work plane (usually 0.85 m from floor) to the luminaire plane (usually the ceiling). A low RCR (under 3) means a shallow, wide room – high CU. A high RCR (over 6) means a tall, narrow room – low CU, more luminaires needed. Suspended luminaires reduce effective ceiling height and change RCR.
What is the Coefficient of Utilisation (CU)? +
CU is the fraction of luminaire output that reaches the work plane. It depends on room geometry (via RCR), ceiling reflectance (typically 0.7–0.8 for white), wall reflectance (0.5 for light coloured), and floor reflectance (0.2). Manufacturers provide CU tables for their luminaires. For direct downlights in a typical office: CU ≈ 0.55–0.70. For indirect/uplighting: CU ≈ 0.30–0.45.
Can I use the lux level calculator for outdoor lighting? +
The lumen method is for indoor uniform lighting. For outdoor: car park surface – use the point-by-point method with manufacturer isolux diagrams. Road lighting – use the CIE 115 method with luminance calculations. Sports facilities – use manufacturer's aiming diagrams. However, a simplified lux check using the lumen method works for covered car parks, loading bays, and semi-outdoor spaces.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

💡 Lux Level Calculator
Reference: SP 72 / NBC 2016 Part 8