High bays: how to size a warehouse

A warehouse with nine metres under the trusses has to replace its discharge lanterns. The reflex is to count the existing points and order the same number of LED high bays. The result gives aisles that are fine at floor level and upper rack levels that cannot be read, with forklift drivers coming back down to check a reference.

Height under the trusses and distance to the working plane

The first figure to record is not the floor area but the clear height under the roof structure, then the actual mounting height, once cable trays, the sprinkler network and overhead crane rails have been deducted. It is the distance between the luminaire and the useful plane that drives the rest of the calculation.

The useful plane is not always the floor. In a storage area, it runs over the full height of the racks. In a preparation area, it is at the level of the workstation. Two different useful planes in the same building give two different sizings, and often two families of luminaires.

The EN 12464-1 standard distinguishes these situations. Storage aisles without permanent presence require 50 lux, aisles where personnel move about 150 lux, packing and dispatch areas 300 lux. The French Labour Code also sets its own minimums: 60 lux in warehouses, 120 lux in premises used for work, 40 lux in internal traffic routes.

Rack aisles: lighting the floor or lighting the levels

In a rack aisle, horizontal illuminance on the floor is not enough. The operator reads a label placed vertically, sometimes four metres up, sometimes just above the floor. The useful criterion is vertical illuminance on the face of the pallets.

A wide-beam luminaire placed in the centre of the aisle gives a good level on the floor and leaves the upper levels in the shadow cast by the pallets themselves. A luminaire with an elongated distribution, oriented along the axis of the aisle, lights both faces over the full height, which completely changes the legibility of the locations.

The resulting layout rule is simple: the luminaires follow the aisles, not a regular grid calculated on the floor area of the building. When the storage plan changes, the layout must be able to follow, which argues for flexible, removable connections. Luminaires designed for industrial warehouses are almost always offered with several distributions for this reason.

Choosing the beam angle according to height

The beam angle is chosen according to the mounting height and the geometry of the room, never according to the power. The higher the luminaire, the narrower the beam must be to concentrate the flux on the useful area instead of lighting the walls.

| Mounting height, order of magnitude | Type of beam | Typical use |

| --- | --- | --- |

| up to about 6 metres | wide | workshops, preparation areas, indoor docks |

| from about 6 to 10 metres | medium | ordinary warehouses, mixed storage and handling areas |

| beyond about 10 metres | narrow | high-bay storage, long-span halls |

These ranges are orders of magnitude intended to frame an initial selection. The final setting is made by calculation, with the real reflectance values of the walls, racks and floor, which change everything in a dark building.

Round high bay or suspended linear: deciding between them

The round high bay produces a circular patch. It suits open areas, indoor docks and surfaces without vertical obstacles. The suspended linear produces a continuous band: it follows the aisle and lights both rack faces evenly.

| Criterion | Round high bay | Suspended linear |

| --- | --- | --- |

| Shape of the area covered | circular patch | continuous band along the axis |

| Narrow rack aisles | frequent cast shadows at the top | even overlap on both faces |

| Open areas and indoor docks | simple grid layout | less obvious division |

| Relocation after rearrangement | moved point by point | linking to be redone section by section |

| Maintenance | individual replacement | intervention by section |

Uniformity in aisles and preparation areas

Uniformity U0 is the ratio between minimum illuminance and average illuminance over the area considered. It is what decides real comfort: an aisle with a correct average but high contrast is more tiring than an aisle that is slightly less lit but even.

EN 12464-1 associates a uniformity value with each situation. The task areas of packing and inspection stations are the most demanding, with a colour rendering of at least Ra 80 in addition. Circulation areas tolerate more variation, provided no abrupt break appears at the end of an aisle.

Fixing, cable trays and quick connection

The fixing method determines the installation cost as much as the price of the luminaire. Suspension by cable, hook on a purlin, rigid rod, fixing on a cable tray: each solution requires a verified anchor point and load transfer documented by the structural design office.

Connection by prefabricated connector reduces the time spent in the cherry picker and makes the intervention safer. It also makes later relocations easier, which are frequent in a logistics building whose storage plan changes with its customers.

In high-ceiling spaces, this point becomes decisive: every cherry picker descent costs operating time and requires a clear area on the floor.

Detection per aisle and management of little-used areas

A warehouse almost always includes little-used aisles and buffer storage areas. Lighting them permanently at working level is a direct waste, of no benefit to anyone.

Detection per aisle, while maintaining a standby level, solves the problem without creating a black hole effect at the end of the bay. The setting is made on site, by observing the real speed of the forklifts: a time delay that is too short switches on and off in front of the operator, which invariably leads to the detector being disabled after a few weeks.

Classic mistakes in a like-for-like replacement

• Taking the existing number of points without checking that the original layout matches the current racks.
• Choosing a wide beam by default, which empties the upper levels and lights the walls.
• Neglecting vertical illuminance, the only useful criterion for reading picking locations.
• Forgetting the areas where the mounting height changes, between conventional storage and high-bay storage.
• Ordering before having surveyed the clear height under the technical obstacles actually in place.

Before fixing a quantity, a photometric study with a simulation of the building validates the layout on the real storage plan, and an audit of the existing installation gives the condition of the supports, circuits and protection devices.

Start by surveying, plan in hand, the mounting height available aisle by aisle and the height of the highest pallet level.

Then choose the equipment in the high bays category.

Further reading: Car park lighting: height, layout and uniformity and Office lighting: LED panel or linear pendant. Reference: NF EN 12464-1 standard on indoor workplace lighting (AFNOR).

In the Rexylum catalogue: UFOBAY UB16 · High-Performance LED High Bay and HB-F16 LED LINEAR HIGH BAY.