Written by Chris Bond, a lighting professional with 18 years of industry experience
Lux (symbol: lx) is the SI unit of illuminance — the measure of how much light falls on a surface. One lux is equal to one lumen per square metre. In plain terms, it tells you how brightly lit a surface actually is, not just how much light a fitting emits.
The word comes from the Latin for light, and it's the unit you'll see in lighting design specifications, Australian Standards documents, and workplace safety requirements. When an engineer specifies "300 lux at bench height" for a workshop, they're describing the amount of light hitting the work surface — not the wattage of the fittings or the lumens in the box.
This distinction matters enormously in practice. A 1000 lumen downlight directly above your desk will produce very different lux levels depending on how high the ceiling is and how reflective the surfaces around it are. Lux is the number that captures the real-world result.
These three terms are related but measure different things, and they're commonly confused even by people who work with lighting regularly.
Lumens measure the total amount of visible light emitted by a source in all directions. It's the number on the LED downlight box. A 13W LED downlight might produce 1100 lumens. That's the raw output of the fitting — it says nothing about how that light is distributed or how brightly it lights a specific surface.
Candela measures luminous intensity — how much light is emitted in a specific direction. A spotlight with a narrow beam concentrates its lumens into a small angle, producing a high candela value in that direction. The same fitting spread wide would have a lower candela value. Candela is most useful for evaluating directional fittings like spotlights, track lights, and luminaires with specific beam angles.
Lux is what you actually experience. It's the illuminance at the point where light lands. This is the number that determines whether a space feels dim or well-lit, whether it meets a safety standard, or whether it's appropriate for the visual task at hand.
The relationship between these units: if you have a source emitting 1 candela uniformly in all directions, it produces 1 lux on every point of a sphere with a 1-metre radius surrounding it. Spread that same light over a 2-metre radius sphere and the lux drops to 0.25 lx — the inverse square law in action.
Different tasks require very different amounts of light. Reading fine print, performing surgery, and walking down a corridor all have different illuminance requirements. The table below covers the most common residential, commercial, and industrial settings.
| Space / Task | Recommended Lux | Notes |
|---|---|---|
| Outdoor pathway / garden | 5–50 lx | Safety and ambience; lower end for decorative, higher for security |
| Bedroom (general) | 100–150 lx | Relaxed environment; dimmable recommended |
| Living room (general) | 150–200 lx | Higher for reading zones |
| Reading / desk work | 300–500 lx | Task lighting required at the reading surface |
| Kitchen benchtop | 300–500 lx | Under-cabinet LED strips are ideal for this |
| Bathroom vanity | 300–500 lx | At face height; avoid shadows from above-only lighting |
| Office (open plan) | 320–500 lx | AS/NZS 1680.2.2 specifies 320 lx minimum for office work |
| Retail shop floor | 500–1000 lx | Higher for display areas and fitting rooms |
| Workshop / trade bench | 500–750 lx | Fine detail work may need 1000+ lx |
| Hospital / clinical areas | 500–1000 lx | Examination areas up to 10,000 lx |
| School classroom | 300–500 lx | Uniform distribution across desk surfaces |
| Car park (indoor) | 75–100 lx | AS/NZS 1158.3.1 governs car park lighting |
| Emergency exit signage | 10 lx minimum | AS 2293 requirement at floor level |
In Australia, workplace lighting is governed primarily by the AS/NZS 1680 series — Interior and Workplace Lighting. This standard is referenced by SafeWork Australia and is the basis for workplace lighting compliance in most commercial and industrial projects.
The key parts of the standard most relevant to building projects are:
The standard specifies maintained illuminance — the average lux level after accounting for lamp depreciation and dirt accumulation over time. This means the design target is typically 25–30% higher than the maintained value to allow for the light output dropping as the fitting ages.
For residential projects, there's no mandatory compliance standard in the same way. However, the AS/NZS 1680.2.1 recommendations for domestic dwellings are widely used by lighting designers as a benchmark and are a sensible target for any renovation or new build.
The most accurate way to measure lux is with a calibrated lux meter (also called an illuminance meter or light meter). These devices use a photodiode sensor to measure the light falling on the sensor surface, and display the result directly in lux.
Professional lux meters cost from around $80 for a basic unit to several thousand dollars for a calibrated research-grade instrument. For most residential and small commercial work, a meter in the $100–$300 range gives adequate accuracy. Hold the sensor at the working plane height — typically 800mm above the floor for a desk or bench — and take readings at multiple points to get an average.
Most smartphones have a light sensor (used for automatic brightness adjustment), and there are apps that read it and display an approximate lux value. The accuracy varies significantly between phone models because the sensors are calibrated for screen brightness control rather than photometric measurement. Treat smartphone lux readings as a rough guide only — they can be 20–40% off from true illuminance, sometimes more.
For a more thorough assessment of a room, lighting engineers take measurements on a grid — typically at 0.5m or 1m intervals across the floor or working plane. This reveals hotspots and dark zones, and allows calculation of the uniformity ratio. For a desk layout in an office, measurements should be taken at the actual desk surface height with the screen and task lighting in their normal positions.
Achieving a target lux level isn't just about choosing a bright-enough fitting. Several factors determine how much light actually arrives at a surface:
Light intensity follows the inverse square law — double the distance from the source to the surface, and the lux drops to a quarter. This is the single biggest variable in most residential spaces. A downlight at 2.4m ceiling height produces significantly higher lux at desk level than the same fitting at 3.2m.
Light bounces. A room with white walls, light-coloured floors, and a white ceiling will have substantially higher ambient lux than a room with dark surfaces, even with identical fittings. Lighting designers assign reflectance values to surfaces — typically 0.7 (70%) for ceilings, 0.5 for walls, and 0.3 for floors as starting assumptions for a typical interior. Dark feature walls or timber floors can significantly reduce these values and require more fittings to compensate.
A narrow-beam downlight (15–25°) concentrates light directly below it, producing high lux in a small circle. A wide-beam downlight (60–90°) spreads light over a larger area, reducing the peak lux but improving uniformity. Most residential downlights sit between 36° and 60° beam angle.
LED fittings don't fail suddenly like old halogen lamps — they gradually dim over time. A quality LED fitting is rated to 70% of initial output (L70) after 50,000 hours. Budget fittings may reach L70 much sooner. If you design for a certain lux level when the fittings are new, expect that level to drop over the life of the installation.
Fittings collect dust, insects, and grime. A fitting in a dusty workshop environment can lose 10–20% of its output within a year if not cleaned regularly. The maintenance factor used in professional lighting calculations accounts for this — typically 0.8 for clean indoor environments.
The most common method for estimating average illuminance is the lumen method (also called the zonal cavity method for more complex spaces). For simple rectangular rooms with a uniform fitting layout, it gives a reliable result:
Average lux = (Number of fittings × Lumens per fitting × Utilisation factor × Maintenance factor) ÷ Area (m²)
Working backwards — if you know the target lux level, room area, and typical fitting output, you can calculate how many fittings you need:
Number of fittings = (Target lux × Area) ÷ (Lumens per fitting × UF × MF)
For anything more complex — irregular rooms, multiple fitting types, specific uniformity requirements, or compliance work — a photometric software package (Dialux, Relux, or AGi32) is the appropriate tool. These allow you to import manufacturer IES/LDT files and model the actual distribution of light from specific products.
For residential and small commercial work, however, the lumen method combined with a lux meter for verification covers the vast majority of situations you'll encounter.
Use the free LightTools Lux Calculator to find out how many fittings you need to hit your target illuminance.
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