Фотометрическое моделирование

A lighting design that is not simulated is an estimate with a confidence interval nobody has calculated. Photometric simulation converts a fixture’s measured light distribution into a predicted illuminance map of the actual space, and it is the only practical way to check uniformity, glare and compliance before the fixtures are ordered. This white paper walks through the working sequence used in the three dominant tools, DIALux evo, AGi32 and Relux, and identifies which inputs actually move the result.

1. What the simulation actually computes

All three tools perform the same underlying calculation: they integrate the flux emitted by each luminaire, weighted by its intensity distribution and the distance and orientation relative to every point in the calculation grid, and then apply the surface reflectance to account for inter-reflection. The output is an illuminance value at each grid point, plus derived metrics such as uniformity and glare index.

Understanding this matters because it identifies the five inputs that govern the answer:

A common and expensive error is to tune the fixture count while leaving the maintenance factor at its default of 0.80. For a high-bay installation in a dusty foundry, the correct factor may be 0.60, which increases the required fixture count by a third. The maintenance factor is a design decision, not a software default.

2. The seven-step workflow

The sequence below applies to all three tools with only the menu names differing.

1. Create the room. Enter the exact geometry: length, width and height to the underside of the structural slab, not to the ceiling grid. Record the work-plane height, which in industrial spaces is the task surface (typically 0.80 m in offices, but 0 m or 0.20 m in warehouses where the floor is the task).
2. Assign surface materials. Set ceiling, wall and floor reflectance. Defaults are acceptable for offices; for a cleanroom with high-reflectance epoxy floors or a dark foundry interior, replace them. The difference between total reflectance and near-zero reflectance can shift indirect illuminance by a factor of two.
3. Import the photometric file. Use the IES or LDT file supplied with the fixture, not a generic distribution. If the file is missing, request it: a real file from Z-16 or Z-13 carries measured intensity at hundreds of angles, while a synthetic distribution carries the designer’s guess.
4. Place the luminaires. Enter the mounting height, spacing and orientation. Run at least two layouts so the uniformity comparison is meaningful.
5. Define the calculation grid. Set grid spacing fine enough to reveal non-uniformity: a spacing no coarser than 0.5 m for task areas, and always an odd number of grid points so that the centre point is included.
6. Set the maintenance factor. Derive it from the luminaire maintenance factor and the room surface maintenance factor, or take the value specified by the client’s standard.
7. Read the results. Report average illuminance, minimum, uniformity U0 (E_min / E_avg), and the glare metric. A single average figure conceals the failure modes of interest.

3. Reading the illuminance grid

The simulation output that matters most is the spatial distribution, not the average. The curve below shows a cross-section through a warehouse aisle at two different mounting heights, holding fixture count constant.

The shape of this curve is the whole argument for co-designing mounting height with beam angle. Raising the fixture from 6 m to 12 m reduces peak illuminance by roughly a factor of four in the inverse-square region, and simultaneously flattens the profile, so that neither the peak nor the uniformity target is met. Adding fixtures at the higher mounting height restores the average but not the uniformity, because the spacing needed for uniformity scales with height.

4. Uniformity versus spacing-to-height ratio

The spacing-to-height ratio (SHR) is the design variable that couples illuminance level to uniformity, and it is the fastest sanity check available before running a full simulation. The curves below show the relationship for three distributions.

Read the curves at the 0.40 threshold. A 60° distribution holds U0 above 0.40 only up to an SHR of about 0.9, while a 120° distribution holds it to about 1.3. This is why Z-16 high-bay luminaires are commonly offered with two optical variants: the narrow version for tall spaces where the ceiling height itself fixes a low SHR, and the wide version for lower spaces where fixture count must be minimised. Selecting the optic without checking the SHR is the most frequent cause of a simulated design that looks acceptable on average and fails the uniformity requirement.

5. Where the three tools differ in practice

The tools compute the same physics; they differ in workflow and in the accompanying libraries.

For projects requiring both EN 12464 and GB 50034 compliance, run the calculation once and then compare the reported metrics against both standards’ limits rather than re-simulating: the physics does not change with the standard, only the acceptance threshold does.

6. Validation: making sure the simulation is trustworthy

Simulation output should never be delivered without a validation step, because a single mis-entered parameter can produce a confident and completely wrong result.

The last row deserves emphasis. The purpose of simulation is to predict the installed result, so a measurement after commissioning closes the loop. Where measured illuminance deviates by more than ten percent, the usual causes in order of likelihood are: incorrect mounting height as built, a maintenance factor that does not match the actual cleaning regime, an incorrect photometric file, and dirty or aged luminaires during measurement.

7. Deliverable set for a design submission

A complete photometric submission for a commercial or industrial project normally contains the following documents. Specifying them up front avoids rework at the approval stage.

• Room summary with geometry, reflectance and work-plane height
• Luminaire schedule with photometric file references, flux and power
• Layout drawing showing positions and spacing
• Illuminance grid with values, and a colour or contour map
• Uniformity and glare summary against the governing standard
• Specific power (LPD) calculation
• Maintenance factor derivation

8. Conclusion

Photometric simulation is a deterministic calculation that becomes unreliable only through its inputs. For Z-16 high-bay, Z-13 cleanroom and Z-15 tri-proof installations, the practical sequence is: obtain the real IES file, derive the maintenance factor from the actual environment, choose the optic by checking the spacing-to-height ratio against the uniformity target, and validate the result by measurement after commissioning. Following that sequence converts a simulation from a compliance formality into a procurement decision.

8. Production commissioning: from prediction to measurement

The measurement step is where a simulation programme either earns its credibility or loses it, so it deserves its own procedure rather than being treated as an afterthought. Three conditions must be controlled before any reading is taken.

Burn-in before measurement. New LED luminaires settle for the first 100 hours as the phosphor and encapsulant reach thermal equilibrium and the drive electronics stabilise. Measuring before this point reads high and produces an optimistic comparison. The standard practice is to operate the installation for at least 100 hours, or to apply a documented burn-in correction, before commissioning measurements.

Meter calibration and cosine response. A calibrated illuminance meter with a photopic-corrected detector is the minimum requirement. Probes without a cosine corrector over-read at oblique incidence, which biases any reading taken off-axis. Verify the calibration certificate date and confirm the meter is within its validity window before the survey.

Measurement grid identical to the simulation grid. If the simulation used a 0.5 m grid with an odd number of points, the survey must use the same grid. Comparing a fine simulated grid against a coarse measured grid creates apparent deviations that are artefacts of the comparison rather than real discrepancies.

The table above is diagnostic rather than exhaustive, but it captures the order of likelihood. In field investigations of commissioning shortfalls, mounting height and maintenance factor account for the majority of genuine deviations, while meter errors and pre-burn-in measurements account for most of the apparent ones.

10. Referenced standards

• IES LM-79 — Approved method: electrical and photometric measurements of solid-state lighting products
• CIE 154 — The maintenance of outdoor lighting systems
• CIE 97 — Maintenance of indoor electric lighting systems
• EN 12464-1 — Light and lighting: lighting of work places, indoor
• EN 12464-2 — Light and lighting: lighting of work places, outdoor
• GB 50034 — Standard for lighting design of buildings
• IES LM-63 — Standard file format for electronic transfer of photometric data

11. Contact us

QUEENDOM supplies IES photometric files for the lighting range and can provide reference layouts for high-bay, cleanroom and tri-proof applications. Contact the lighting engineering group with the room dimensions, mounting height and target illuminance, and the appropriate photometric file and optic variant will be supplied for simulation.

Related products and applications

The luminaires used in the simulation workflow are available in the following families.

• High-bay luminaire (Z-16)
• Industrial high-bay luminaire (Z-13)
• Tri-proof luminaire (Z-15)
• Greenhouse top light (Z-09)
• Application overview: Lighting application solutions
• More technical papers: Lighting knowledge resources