Uniformité des luminaires high-bay

Industrial lighting specifications that quote only average illuminance routinely fail on site, because the parameter that operators actually experience is uniformity. A warehouse aisle at 300 lx average with a 4:1 max-to-min ratio produces alternating pools of glare and shadow that slow picking and increase error rates, even though the average meets the standard. This white paper explains how mounting height, beam angle, spacing and fixture output interact to set both average illuminance and uniformity ratio U0, and how QUEENDOM’s Z-16 High-Bay Industrial and Mining luminaire is specified for those conditions.

1. Why uniformity matters as much as illuminance

EN 12464-1 sets both an average maintained illuminance and a uniformity ratio for each task area, and the uniformity requirement is the one that constrains the layout. Three definitions must be kept distinct:

• U0 (overall uniformity) — the ratio of minimum to average illuminance over the task area, E_min / E_avg.
• Ud (diversity) — the ratio of minimum to maximum illuminance, E_min / E_max.
• E_avg — the arithmetic mean illuminance over the reference surface.

A design that satisfies E_avg but ignores U0 will typically show U0 between 0.15 and 0.25 in a tall space, well below the 0.40 to 0.60 that EN 12464-1 requires for most industrial tasks. The table below gives representative requirements for common industrial areas.

2. The geometry that drives uniformity

Illuminance from a point source on an inclined surface falls with the inverse square of the distance and is modulated by the cosine of the incidence angle. In a high-bay installation this produces a characteristic scallop pattern: a bright disc directly under each fixture and a dimmer region midway between fixtures. The uniformity ratio is therefore a function of three geometric quantities.

Spacing-to-height ratio (SHR). The ratio of centre-to-centre fixture spacing to mounting height above the reference plane. Higher SHR means more scalloping. As a rule, keeping SHR below 1.0 preserves acceptable uniformity with narrow-beam optics, while SHR above 1.3 almost always requires a wider beam or a dimmed interleaved layout.

Beam angle. A 60° optic concentrates flux into a small footprint and produces excellent uniformity inside that footprint but leaves the inter-fixture region dark when spacing is large. A 120° optic spreads energy broadly and raises U0 at high SHR, at the cost of more light spilling beyond the task area.

Mounting height. Raising fixtures increases the illuminated footprint of each unit and therefore improves overlap, but it also reduces delivered illuminance by the inverse square law. Doubling mounting height requires roughly four times the flux per fixture to hold the same average illuminance.

3. Parameters and selection

Z-16 is available with three interchangeable optic distributions, and the choice among them is driven almost entirely by the required SHR rather than by the illuminance target.

The table below converts beam angle and mounting height into the recommended maximum spacing that holds U0 ≥ 0.40.

3.1 Uniformity versus spacing-to-height ratio

The curve below shows how U0 falls as SHR increases, for each of the three optics at a 6.0 m mounting height. The red line marks the EN 12464-1 threshold of 0.40 for general industrial work areas.

4. Illuminance calculation method

The lumen method is the standard first-pass calculation for a high-bay grid, and it is adequate provided the maintenance factor and the utilisation factor are chosen honestly.

E_avg = (N × Φ × UF × MF) / A

where N is the fixture count, Φ is the initial luminous flux per fixture in lumens, UF is the utilisation factor for the room, MF is the maintenance factor, and A is the reference plane area in square metres.

Utilisation factor. The fraction of emitted lumens that reach the reference plane. It depends on room index, surface reflectances and beam angle. For a high-bay hall with a room index above 3.0 and 60° optics, UF typically sits between 0.75 and 0.85. For 120° optics in a low room index space, UF falls to 0.55 to 0.65 because more light hits the walls.

Maintenance factor. The product of lamp lumen depreciation, luminaire dirt depreciation and room surface dirt depreciation. In a foundry or mining environment with IP65 luminaires on a 12 month cleaning cycle, MF of 0.65 to 0.72 is realistic. In a clean warehouse on a 24 month cycle, 0.80 is achievable.

The worked example below covers a 30 m × 20 m × 8 m machine hall served by Z-16 150 W at 60°.

The deliberate over-provision followed by dimming is standard practice in industrial high-bay work, because it allows the installation to maintain the target illuminance as the maintenance factor decays and because it leaves headroom for future layout changes.

4.1 Required fixture count versus mounting height

The curves below show the fixture count required to hold 300 lx maintained in a 600 m² hall as mounting height varies, for the three Z-16 power classes.

5. Vertical illuminance and the rack-face problem

Warehouse aisles are often specified on horizontal illuminance alone, and then fail because the task is reading labels and distinguishing cartons on a vertical rack face. Vertical illuminance at the rack face depends on the horizontal offset between the fixture and the rack, and on the downward flux distribution of the optic.

Two layout rules follow. First, offset the fixture line toward the aisle centre rather than directly over the rack, so that both rack faces receive comparable vertical illuminance. Second, prefer a wider optic in narrow aisles, because the wider distribution lifts the vertical component at moderate angles without producing the severe glare that a narrow optic aimed sideways would create.

6. Common mistakes and how to avoid them

7. Verification and test methods

1. Photometric verification per IES LM-79 — measure luminous flux, efficacy, CCT and CRI at thermal equilibrium on a representative sample of each power class.
2. Illuminance grid measurement — after installation, measure illuminance on a grid at no more than 1 m spacing at the working plane, and compute E_avg, E_min and U0 from the measured values rather than from the design model.
3. Vertical illuminance spot check — measure vertical illuminance at 1.5 m above the floor on both rack faces at three positions per aisle.
4. Glare assessment — compute UGR for the as-built layout using the luminaire photometric file, and confirm it against the EN 12464-1 limit for the task.
5. Lumen maintenance projection per IES TM-21 — use IES LM-80 data to project flux at 50,000 hours and confirm the maintenance factor adopted in the design.

8. Conclusion and selection guidance

For machine halls and general industrial bays at 6 to 10 m mounting height with spacing-to-height ratio below 1.0, Z-16 High-Bay at 150 W with the 60° optic delivers 24,000 lm per position and holds U0 above 0.50 in a well-laid-out grid. Where the hall is tall and the grid must be wide, move to the 120° optic and accept a lower UF in exchange for a higher U0. Where a single row of fixtures must cover a large span and the power budget allows, Z-16 at 200 W reduces fixture count and installation labour, at the cost of coarser dimming granularity across the hall. In every case, size the grid on the uniformity curve first, apply a realistic maintenance factor, and verify U0 on the installed grid rather than trusting the model.

9. Adjacent areas and fixture families

High-bay halls rarely exist in isolation. Two neighbouring fixtures from the same industrial range are routinely specified alongside Z-16, and the interfaces between them are where uniformity is most often lost.

Wash-down and food-grade zones adjacent to a machining hall. Where the high-bay hall opens into a wash-down or food-processing area, the luminaire must survive routine high-pressure cleaning. Z-15 Tri-proof luminaires at IP65 suit these transition zones, and the important design point is the illuminance step across the doorway: if the wash-down area is lit to 200 lx and the machine hall to 300 lx, the transition band should be lit to the mean of the two so that operators do not adapt repeatedly. Because Z-15 and Z-16 share the same IP65 construction and dimming interface, they can be placed on the same control zone.

Clean and inspection areas. Where high-bay storage adjoins a controlled-environment inspection room, Z-13 Cleanroom LED Panel covers the enclosed area at the much higher uniformity that a particulate-controlled room requires. The interface concern is reflectance: a rack face at 0.20 reflectance in the hall adjacent to a 0.80 reflectance clean-room wall produces a visible brightness discontinuity, so the connecting corridor should be finished with an intermediate reflectance surface.

10. Referenced standards

• EN 12464-1 — Light and lighting of work places, Part 1: Indoor work places
• EN 12464-2 — Light and lighting of work places, Part 2: Outdoor work places
• IES LM-79 — Approved Method: Electrical and Photometric Measurements of Solid-State Lighting Products
• IES LM-80 — Approved Method: Measuring Luminous Flux and Color Maintenance of LED Light Sources
• IES TM-21 — Projecting Long Term Lumen, Photon and Radiant Flux Maintenance of LED Light Sources
• CIE 154 — The Maintenance of Outdoor Lighting Systems
• IEC 60598-2-1 — Luminaires, Part 2-1: Particular requirements for fixed general purpose luminaires

11. Contact us

QUEENDOM supplies the Z-16 High-Bay Industrial and Mining luminaire from stock in 100 W, 150 W and 200 W classes with 60°, 90° and 120° optics, IP65 and IK08 construction, and 0–10 V or DALI-ready dimming, together with the Z-15 Tri-proof and Z-13 Cleanroom LED Panel families for adjacent zones. Contact our industrial lighting engineering group for photometric files, grid layout calculations and sample quantities.

Related products and applications

The high-bay luminaires discussed in this uniformity paper are listed below.

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