Good commercial lighting is not just about powerful luminaires: it’s also about accurately calculating illuminance levels to ensure that the visual experience is comfortable, attractive and compliant with standards. Knowing how to calculate the optimum illuminance for a commercial space can improve the customer experience while optimising energy consumption.
Why calculate the illuminance of a retail space?
Lighting has a direct influence on how a product is perceived, the comfort of visitors and even buying behaviour. A shop that’s too dark is discouraging, while a space that’s too bright is tiring for the eye and degrades colours.
Calculating the right level of illumination (expressed in lux) helps to :
- ensure optimum product visibility;
- create an atmosphere consistent with the brand’s positioning;
- guarantee compliance with standards (EN 12464-1 in Europe);
- reduce power consumption without compromising visual quality.
The units and concepts you need to know
Before moving on to the calculations, it’s important to distinguish between the terms used:
- Lumen (lm): luminous flux emitted by the source.
- Lux (lx): illuminance received on a surface (1 lux = 1 lumen/m²).
- Watt (W): electrical power consumed.
- Luminous efficiency: ratio between lumens emitted and watts consumed (lm/W).
The lux level to be achieved depends on the type of business and the nature of the products on display.
Recommended lux levels according to the type of space
| Area / activity | Illuminance level (lux) | Remarks |
|---|---|---|
| Circulation, main aisles | 200-300 lx | Functional, uniform lighting |
| Shelves, displays | 500-800 lx | Accentuate contrasts, enhance products |
| Display cases, gondola heads | 1000-1500 lx | Directional or focused lighting |
| Checkouts, work areas | 300-500 lx | Uniform, glare-free lighting |
The simplified method for calculating illuminance
The basic formula used in lighting design is as follows:
E = (Φ × UF × MF) / S
where
- E = average illuminance (in lux)
- Φ = total luminous flux of luminaires (in lumens)
- UF = utilisation factor (depending on the type of luminaire and the geometry of the room)
- MF = maintenance factor (takes account of ageing and soiling)
- S = surface area of the room (in m²)
Example of calculation
For an 80 m² shop requiring 500 lux:
Φ = (E × S) / (UF × MF)
Taking UF = 0.7 and MF = 0.8 :
Φ = (500 × 80) / (0.7 × 0.8) = 71,428 lumens
You will therefore need approximately 71,000 lumens spread over the entire surface, i.e. 10 luminaires of 7,000 lm each.
Factors influencing the result
The theoretical calculation needs to be adjusted according to a number of parameters:
- Ceiling height: the higher the ceiling height, the more lumens are required to compensate for losses.
- Surface reflectance: light walls reflect light, dark surfaces absorb it.
- The type of optics: a narrow beam focuses the light on a precise area, a wide beam diffuses it more evenly.
- Colour temperature: warm white (3000 K) creates a welcoming atmosphere, neutral white (4000 K) highlights products more effectively.
Lighting simulation tools
For professional projects, the use of photometric simulation software is essential. Tools such as Dialux or Relux allow you to model the room in 3D, integrate the IES or LDT files of the luminaires and obtain an accurate illuminance calculation based on the actual characteristics of each product.
Benefits of simulation
- Visual validation of lux distribution;
- Avoid areas of shadow or overexposure;
- Optimisation of the number and type of luminaires;
- Reports that comply with indoor lighting standards (EN 12464-1).
Rodalight tips for successful commercial lighting
- Favour modular lighting (dimmable or DALI) to adjust according to the season and the products.
- Combine ambient lighting and accent lighting to create visual highlights.
- Use high CRI sources (≥90) for accurate colour reproduction.
- Check the maintenance factor regularly: cleaning or partial replacement can restore up to 20% of lost brightness.
Things to remember
- A good illuminance calculation guarantees comfort, attractiveness and compliance.
- The lux level depends on the type of area and the nature of the products.
- Tools such as Dialux provide a realistic, optimised simulation.
- Properly dimensioned lighting enhances the space while reducing energy consumption.
The Rodalight team
