Warehouse Lighting Design: High-Bay LEDs, Rack Aisles and Daylight

Average lux is the wrong headline

Warehouse lighting is usually bought on two numbers: a target lux level and a fitting count. A lighting layout is produced on an empty floor plan, the average lux comes out above the target, and the job is signed off.

Then the racking goes in. Aisles turn out dim at the pick faces, labels at the upper levels are hard to read, drivers squint into bright fittings when they look up, and the lights burn all day in aisles nobody visits. A high average lux across the floor says very little about whether people can see what they are doing. As with offices, lux alone is not enough, and in a warehouse the gap is wider, because the work happens on vertical rack faces at height, often from a moving vehicle.

For an operations head the costs are concrete: picking errors, slower picking, forklift contact with racking, an energy bill for lighting empty aisles, and failed fittings nobody can reach without clearing an aisle.

The racking decides the lighting layout

The single most important input to warehouse lighting is the racking layout. Luminaires in a racked area belong above the aisles, aligned with them, not on a uniform grid across the roof. When racking is moved or added after the lighting is fixed, fittings end up above rack tops, where they light pallets nobody needs to see and leave the aisles dark.

Standards such as IS 3646 (Part 1) and EN 12464-1 tabulate recommended lighting by task and area, including illuminance, uniformity and glare limits. The lighting designer selects the values for each zone; what lux level means, and how it is measured, is explained separately.

Uniformity and glare matter more than brightness

Uniformity is the ratio between the lowest and the average illuminance across an area. Eyes adapt to the general level; what causes trouble is a dark patch in a bright space, where a pallet, a person or a spill disappears. A layout that hits a high average with poor uniformity can be harder to work in than one with a lower, even level.

Glare is the other half. Someone walking rarely looks at a high-bay fitting. A forklift or reach truck driver does, constantly, when placing or retrieving loads at upper levels. An unshielded, high-output source in that line of sight dazzles exactly when precision matters. Luminaire choice, shielding, mounting height and position relative to the aisle direction reduce it, and the standards include glare limits the designer checks.

Colour rendering matters where labels are colour-coded or goods are inspected; the requirement varies by activity.

Flicker is easy to overlook. Poor-quality LED drivers can produce flicker that is barely visible but tiring over a shift, and near rotating machinery it can create a stroboscopic effect that makes moving parts appear slow or still. Driver quality belongs in the specification, not only the luminaire's output.

Mounting height and beam: a fitting is more than its wattage

High-bay luminaires are often compared on wattage and lumen output alone. Two fittings with the same output can perform very differently in the same building, because what decides the result is how the light is distributed from the mounting height to the working plane.

A wide beam from a high roof spreads light across open floor and overlaps evenly between fittings. The same beam over a narrow aisle between tall racks throws most of its light onto the rack tops and the upper pallets, and little reaches the lower rack faces. A narrow or elongated beam aligned with the aisle does the opposite. Mounting height also changes with the roof profile: in a pitched portal frame shed the fittings near the eaves sit lower than those near the ridge, and a layout that ignores this gives bright and dim bands.

That is why a lighting design should come with a calculation for the actual roof, racking and fitting, showing horizontal and vertical light in the aisles, rather than a rule-of-thumb fitting count for the floor area.

Daylight: skylights bring heat as well as light

Translucent roof sheets are a common way to bring daylight into a shed, and in daytime operation they can reduce the need for electric light. Polycarbonate skylight sheets and FRP sheets differ in light transmission, diffusion, ageing and fire behaviour.

The trade-off is heat. A skylight admits solar heat along with light, and on a metal roof in an Indian summer that raises the temperature under the roof in a naturally ventilated shed, or adds to cooling load in a conditioned one. More skylight area is not automatically better. The useful questions are how much area, how evenly it is distributed, whether the sheet diffuses light to avoid hot spots and harsh shadows, and whether the electric lighting actually dims when daylight is sufficient. Without daylight controls, skylights add heat and save nothing.

Translucent sheets are also fragile and are a frequent leak point at laps; both need detailing, and no one should walk on them.

Controls: most aisles are empty most of the time

LED high-bay luminaires switch and dim instantly, which older high-intensity discharge lamps could not do without a warm-up delay. That makes controls practical in a way they were not before.

• Occupancy sensing per aisle lets lighting rise when a vehicle or person enters and fall back when the aisle is empty.
• Daylight sensing dims fittings in zones under skylights or near wall glazing when daylight is enough.
• Zoning and scheduling match lighting to shifts and to areas that are not in use.

ECBC 2017 sets energy efficiency provisions for lighting and controls in buildings within its scope, and lighting power density is the related measure. Sensor positions and time delays need commissioning against real traffic, or lights switch off around a driver.

Maintenance at height

High-bay fittings are typically mounted high above the floor, and every one of them will need attention at some point. Usually that means a mobile elevating work platform, which needs floor space and an aisle wide enough beneath the fitting. Check maintenance access against the racking layout at design, choose fittings with long rated life and replaceable drivers, and specify an IP rating suited to dust and humidity in the building.

Common mistakes

• Designing lighting on an empty floor plan before the racking is fixed.
• Judging the design on average lux without checking uniformity and vertical light on rack faces.
• Wide-beam fittings over narrow aisles, lighting rack tops instead of faces.
• Skylights without daylight controls, adding heat with no saving.
• No occupancy sensing in aisles that are empty most of the day.
• Fittings placed where no platform can reach them.

What to ask your lighting designer

• Which racking layout was the design based on, and is it final?
• What illuminance, uniformity and glare limits were used for each area, from which standard?
• How is vertical illuminance on rack faces checked?
• How will skylights and electric lighting work together?
• Which controls are proposed, and how will they be commissioned?
• How will each fitting be reached for maintenance?

Standards referenced

Recommendations for working interiors in IS 3646 (Part 1); lighting of indoor work places in EN 12464-1; lighting and controls in ECBC 2017; lighting and natural ventilation in NBC 2016, Part 8. Illuminance, uniformity, glare limits and controls for a specific warehouse must be established by the project's lighting designer and services engineer; nothing on this page replaces that design.