Lux to Lumens Converter

Converting lux to lumens requires knowing the area you’re illuminating. Lux measures illuminance (light hitting a surface), whilst lumens measure total light output. Our converter makes this relationship clear and gives you precise results for any lighting project.

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Illuminance (lx)

Area

Area Unit

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Lux to Lumens Conversion Table

Here’s a practical reference showing how lux converts to lumens across different room sizes. These examples assume standard rectangular spaces.

Illuminance (lx)	Area (m²)	Luminous Flux (lm)	Common Application
100	10	1,000	Corridor lighting
200	15	3,000	Lounge or bedroom
300	12	3,600	Office space
500	20	10,000	Kitchen workspace
750	8	6,000	Retail shop floor
1000	5	5,000	Workshop bench

Conversion Formula and Steps

The relationship between lux and lumens is straightforward once you know the illuminated area. Follow these steps to perform the conversion manually.

The Formula

Lumens (lm) = Lux (lx) × Area (m²)

For areas measured in square feet, first convert to square metres by multiplying by 0.092903, or use this formula directly:

Lumens (lm) = Lux (lx) × Area (ft²) × 0.092903

Step-by-Step Process

Measure the illuminance at the surface in lux (using a light metre)
Measure or calculate the total area being illuminated
Ensure your area measurement is in square metres
Multiply the lux value by the area in square metres
The result gives you the total luminous flux in lumens

Worked Example

A kitchen worktop receives 400 lx of illuminance. The worktop measures 3 metres by 2 metres (6 m²). What’s the total light output reaching this surface?

Using the formula: 400 lx × 6 m² = 2,400 lm

The total luminous flux hitting the worktop is 2,400 lumens. This tells you how much light output your fixtures need to deliver to achieve the desired illuminance.

Recommended Lux Levels in the UK

Different spaces require different illuminance levels according to British Standards. Use these guidelines when planning lighting schemes for various environments.

Space Type	Recommended Lux	Lumens Required (10 m²)
Living room	120-200	1,200-2,000
Bedroom	120-200	1,200-2,000
Bathroom	250	2,500
Kitchen	250-500	2,500-5,000
Dining room	500	5,000
Home office	500	5,000
Workshop	500-1000	5,000-10,000
Stairway	100	1,000

Key Differences Between Lux and Lumens

Lux and lumens measure different aspects of light. Here’s what sets them apart and when to use each measurement.

What Lux Measures

Lux quantifies illuminance—the amount of light falling on a surface per square metre. One lux equals one lumen per square metre. It tells you how bright a surface appears and varies with distance from the light source. You measure lux with a light metre at specific locations.

What Lumens Measure

Lumens quantify luminous flux—the total amount of visible light emitted by a source in all directions. This measurement doesn’t change with distance or room size. Manufacturers list lumen output on bulb packaging to indicate total light production.

Why Both Matter

When specifying lighting, lumens tell you what to buy (how bright the bulb is). Lux tells you what you’ll get (how bright the space will be). A 1,000-lumen bulb creates 100 lx in a 10 m² room but only 50 lx in a 20 m² room.

Typical Scenarios

See how lux and lumens work together in everyday British settings. These examples show practical applications you might encounter at home or work.

Home Office Setup

Your desk measures 1.5 m × 0.8 m (1.2 m²). British Standards recommend 500 lx for computer work. You need 500 × 1.2 = 600 lumens focused on your workspace. A desk lamp rated at 800-1000 lumens provides adequate light with some spillage.

Kitchen Renovation

Your kitchen spans 4 m × 3 m (12 m²). Food preparation areas need 500 lx. Required lumens: 500 × 12 = 6,000 lm. You might install four ceiling spots at 1,500 lm each, or two pendant lights at 3,000 lm each, to achieve proper illumination.

Retail Shopfitting

A boutique floor area measures 8 m × 5 m (40 m²). Retail spaces typically need 500-750 lx. At 750 lx: 750 × 40 = 30,000 lumens total. This might require 10 track lights at 3,000 lm each or 6 high-output fixtures at 5,000 lm each.

Light Distribution Factors

Converting lux to lumens gives you a baseline, but several factors affect actual lighting performance. Understanding these helps you plan more accurately.

Ceiling Height

Higher ceilings mean light travels further before reaching work surfaces. The inverse square law applies—doubling the distance quarters the illuminance. A 3-metre ceiling height is standard, but anything above 3.5 m may require more lumens to achieve the same lux at floor level.

Surface Reflectance

Light-coloured walls and ceilings bounce light around, increasing effective illuminance. Dark surfaces absorb light, reducing it. A room with white walls might achieve 500 lx with 20% fewer lumens than the same space painted in dark colours.

Fixture Efficiency

Not all lumens from a bulb reach your workspace. Lampshades, diffusers, and fixture design affect light transmission. A bare bulb delivers nearly all its lumens, whilst a frosted pendant might transmit 70-85%. Factor in a 20-30% loss for typical domestic fixtures.

Units Of Light Conversions

Light measurement involves several related units. Here’s how they connect and when you’ll encounter each in British contexts.

Unit	Measures	Symbol	Relationship
Lumen	Luminous flux	lm	Total light output
Lux	Illuminance	lx	1 lx = 1 lm/m²
Candela	Luminous intensity	cd	Light in specific direction
Foot-candle	Illuminance	fc	1 fc = 10.764 lx
Nit	Luminance	cd/m²	Brightness of surface

FAQs

Can I convert lux to lumens without knowing the area?

No, you can’t. Lux measures light per square metre, whilst lumens measure total light output. Without area, there’s no way to calculate the total. It’s like trying to find distance without knowing speed or time. The area creates the mathematical relationship between these two measurements.

Why do my lighting calculations never match reality?

Several factors create discrepancies. Light absorption by furniture, wall colours, and ceiling height all affect actual illuminance. Fixture efficiency losses mean not all bulb lumens reach your space. Dirt accumulation on fixtures reduces output over time. Professional lighting designers typically add 20-30% extra lumens to account for these real-world losses.

How many lumens does my room need?

First, find the recommended lux level for your room type (see the table above). Measure your room’s area in square metres (length × width). Multiply lux by area to get lumens. For a 4 m × 3 m bedroom (12 m²) needing 150 lx: 150 × 12 = 1,800 lumens total. Divide this among your light fixtures.

Does LED brightness work the same as incandescent?

Lumens measure actual light output regardless of technology. A 1,000-lumen LED produces the same brightness as a 1,000-lumen incandescent bulb. The difference lies in energy consumption—LEDs need far less power to generate the same lumens. Always compare bulbs by lumens, not watts, to ensure equivalent brightness.

What’s the difference between lux and foot-candles?

Both measure illuminance, but lux uses metric units (lumens per square metre) whilst foot-candles use imperial units (lumens per square foot). The UK uses lux in building regulations and British Standards. To convert: 1 foot-candle equals 10.764 lux. Many American lighting specifications use foot-candles, so conversion is sometimes necessary.

How do I measure lux in my space?

You need a light metre (lux metre). These devices measure illuminance at specific points. Position the metre at the height where lighting matters most—typically desk height (75 cm) for offices or counter height (90 cm) for kitchens. Take readings at multiple locations since illuminance varies across a room. Average these readings for overall room brightness.

Can I add lumens from multiple bulbs?

Yes, lumens are additive. Three 800-lumen bulbs provide 2,400 lumens total output. However, the resulting lux depends on how you position the lights. Evenly spaced fixtures create uniform illuminance. Clustered lights create bright spots and shadows. For best results, distribute your total lumens across multiple well-positioned fixtures rather than using one powerful central light.