Understand the difference between lux and lumens for professional lighting design.Complete guide to illuminance vs luminous flux with practical examples, conversions, and UK lighting standards applications.
Understand exactly what lux and lumens measure and why both are essential for professional lighting
Lux measures illuminance - how much light actually reaches and hits a surface. It's measured in lumens per square metre and tells you how bright a surface appears to the human eye.
Lumens measure luminous flux - the total amount of light energy emitted by a source in all directions.It's an absolute measurement that doesn't change with distance or area.
Side-by-side comparison of illuminance (lux) and luminous flux (lumens) for professional understanding
| Property | 🔆 LUX (Illuminance) | 💡 LUMENS (Luminous Flux) |
|---|---|---|
| What it measures | Light hitting a surface Brightness perceived by eye |
Total light output from source Light energy emitted |
| Units | lx (lumens per square metre) | lm (lumens) |
| Distance dependency | ✅ YES - Decreases with distance Follows inverse square law |
❌ NO - Constant regardless of distance Always the same from source |
| Area dependency | ✅ YES - Same lumens over larger area = lower lux | ❌ NO - Total output remains constant |
| UK Standards | ✅ BS EN 12464-1 (workplace) ✅ BS 5266-1 (emergency) ✅ HSE requirements |
❌ Not used in compliance standards Used for fixture specifications |
| Measurement tool | Lux meter / Light meter Measured on-site at surface |
Integrating sphere Laboratory measurement |
| Professional use | ✅ Compliance verification ✅ Workplace assessments ✅ Health & safety |
✅ Fixture selection ✅ Energy calculations ✅ Lighting design |
| Conversion | Lux = Lumens ÷ Area (m²) | Lumens = Lux × Area (m²) |
| Example values | Office: 300-500 lux Retail: 300-750 lux Emergency: 1 lux minimum |
LED bulb: 800 lm Office light: 3000 lm Stadium flood: 50,000 lm |
| What matters to users | ✅ How bright their workspace feels ✅ Can they see properly? ✅ Compliance with standards |
How much electricity used Fixture efficiency Total light availability |
Real-world scenarios showing how lux and lumens work together in professional lighting applications
Requirement: 300 lux for computer work over 20m² office (BS EN 12464-1)
Key Point: UK standards specify lux (what workers experience), but you buy fixtures rated in lumens.
Challenge: Same 3,000 lumen light fitting used in different sized areas
Key Point: Lumens stay constant, but lux changes with area. More area needs more lumens for same lux.
Requirement: 1 lux minimum on 30m escape route (BS 5266-1)
Key Point: Emergency lighting compliance measured in lux, but emergency lights specified in lumens.
Challenge: 200 lux required over 500m² warehouse at 8m height
Key Point: Higher mounting = lower lux from same lumens. Need more lumens or more fixtures.
Scenario: Upgrading from fluorescent to LED while maintaining 500 lux
Key Point: Lux and lumens stay same, but watts reduce.LED efficiency improves lumens-per-watt.
Design Goal: 150 lux for intimate dining atmosphere over 40m² area
Key Point: Multiple small lumens sources can create desired lux level with better light distribution.
Essential conversion formulas and practical calculation methods for professional lighting design
The fundamental relationship between illuminance and luminous flux. Area is always in square metres for metric calculations.
Point source calculation. Lux decreases with square of distance. Same lumens give different lux at different distances.
Converting between metric (lux) and imperial (foot-candles) illuminance units for international projects.
Approximate power consumption based on typical LED (120 lm/W) and fluorescent (80 lm/W) efficacy.
• Office: ~500 lm per m² (including losses)
• Retail: ~750 lm per m² for 300 lux
• Warehouse: ~300 lm per m² for 150 lux
• Emergency: ~2 lm per m² for 1 lux
Understand which measurement to focus on for different aspects of lighting projects and compliance
UK lighting standards (BS EN 12464-1, BS 5266-1) specify requirements in lux.Use lux measurements for compliance verification and health & safety assessments.
Light manufacturers rate fixtures in lumens.Use lumen output to select appropriate fittings and calculate how many fixtures you need.
Lux meters measure actual illuminance on surfaces.Use lux readings to verify installations meet design requirements and UK standards.
Calculate power consumption and running costs based on lumens per watt efficiency of different technologies (LED, fluorescent, etc).
Start with lux requirements (standards), calculate lumens needed, select fixtures with adequate lumen output, then verify with lux measurements.
BS 5266-1 specifies minimum lux levels. Test with lux meter to ensure compliance, but select emergency fittings based on lumen output.
Track lumen depreciation over time.LED lumens reduce gradually, affecting lux levels.Plan maintenance based on maintaining minimum lux.
Compare lumens per pound and lumens per watt for value analysis.Present lux improvements to clients for productivity and safety benefits.
HSE requires adequate lighting for workplace safety.Measure lux levels to demonstrate compliance with minimum illuminance requirements.
Complete toolkit for measuring, calculating and documenting both lux and lumens in professional projects
Professional iPhone lux meter for on-site illuminance measurement.Verify your lumen calculations by measuring actual lux levels achieved.
Convert between lux requirements and lumens needed.Essential for fixture selection and compliance verification.
Determine required lux levels per UK standards, then calculate corresponding lumens needed for your projects.
Generate PDF certificates documenting both lux measurements and fixture specifications for complete compliance records.
Document both lux measurements and fixture details in comprehensive lighting surveys with GPS and photos.
Manage lighting projects from lumen calculations through lux verification to final certification and maintenance scheduling.
Common questions about understanding and using lux and lumens in professional lighting work
Lumens measure total light output from a source (luminous flux), while lux measures illuminance - how much light reaches a surface per square metre. 1 lux = 1 lumen per m². Lumens are about the light bulb, lux is about what you see on your desk.
To convert: Lumens = Lux × Area (m²).For example, 300 lux over 20m² = 6,000 lumens. To convert back: Lux = Lumens ÷ Area (m²).The conversion requires knowing the surface area being illuminated.
Both are important but for different purposes. Lux is crucial for compliance (BS EN 12464-1 specifies lux requirements), while lumens are needed for fixture selection. UK lighting standards are specified in lux, but you buy light fittings rated in lumens.
BS EN 12464-1 requires 300 lux for computer workstations and 500 lux for general office work.These are illuminance (lux) measurements at the working plane, not luminous flux (lumens) from the light fittings.
For 300 lux: Lumens needed = 300 × room area (m²).For a 20m² office: 300 × 20 = 6,000 lumens minimum.In practice, you need more lumens from fixtures due to efficiency losses - typically 10,000-12,000 lumens total.
The lux and lumens values remain the same regardless of light source type.However, LED lights typically produce more lumens per watt (80-150 lm/W) compared to fluorescent (50-100 lm/W), so you need fewer watts to achieve the same lux levels.
Lux depends on distance and area. The same fixture (constant lumens) will give higher lux when closer to the surface or covering a smaller area.This is why desk lamps give more lux than ceiling lights with the same lumens.
No. Emergency lighting compliance (BS 5266-1) is specified and measured in lux, not lumens.You need a lux meter to verify 1 lux minimum on escape routes. However, you select emergency fittings based on their lumen output.
Room surfaces don't change the lumens from your fixtures, but they significantly affect lux levels.Light-coloured walls reflect more light, increasing lux readings. Dark surfaces absorb light, reducing the lux achieved from the same lumens.
Use a lux meter app to measure different scenarios: same light source at different distances, different room sizes, various surface colours.See how lumens stay constant while lux changes. This hands-on experience makes the theory clear.
Put your lux vs lumens knowledge into practice. Download our professional lux meter app to measure actual illuminance and verify your lighting calculations meet UK standards.
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