A 3PL operator near Rotterdam lit 14,000 m² of racking with 150W units at ten metres. The floor measured 320 lux, above the 100 lux the standard asks for. The fourth rack level measured 55 lux. Pickers were reading labels with a phone torch, and mis-picks ran at 2.8% for six months. The audit that finally forced a fix did not test the floor. It tested the rack face, with the meter held vertically. That change in measurement method is the difference between a compliant LED high bay light layout and one that actually works.
Why Floor Lux Passes and Rack Faces Stay Dark
A horizontal lux meter reads light arriving on a flat surface. A rack face is vertical, and light from a fixture directly above arrives at a shallow angle. Cosine law does the rest: at 45° off the fixture axis, 70% of the intensity reaches the surface; at 70°, 34%. An LED high bay light layout can hit 300 lux on the floor and still leave 50 to 70 lux on the third and fourth levels.
Standards do not rescue you here. EN 12464-1 asks 100 lux horizontal for storage areas, with 0.40 uniformity and UGR 25. It sets no vertical target, so the operator does: 150 to 200 lux on picking faces, measured vertically, at every level you pick from. A 200 lm/W LED high bay light buys you efficiency, but lumens do not fix geometry. The wrong position loses more light than the right chip gains.
The Geometry That Decides Vertical Light
Three things control vertical illuminance: where the fixture sits relative to the aisle, how it is tilted, and what optic it carries.
An LED high bay light centred over the rack beam spends most of its output on the top of the beam and the face directly below it. Move it over the aisle and both faces receive light, but the distance to each face grows, so intensity drops with the square of that distance.
Tilt is the cheap fix. Angling the LED high bay light 10° to 15° toward the picking face lifts vertical illuminance there by roughly a quarter, at the cost of the opposite rack. On a two-sided aisle, alternate the tilt down the run, or specify asymmetric aisle optics that push light sideways without wasting it on the ceiling.
Beam angle sets the working height. A 60° optic suits mounting above 12 m, 90° covers 8 to 12 m, and 120° belongs below 8 m or over open floors. Putting a 120° LED high bay light at 9 m over a rack aisle sends light into the eyes of anyone 20 m away and leaves the upper shelf dim.
Spacing, Mounting Height and the S/MH Number
Spacing to mounting height, or S/MH, is the fastest check on a layout. Divide the fixture spacing by the mounting height above the work plane. For 90° optics, 0.9 to 1.1 works. For 60°, 0.6 to 0.8. For 120°, 1.2 to 1.4. Push past those numbers and the pool of light under each LED high bay light separates, showing as dark bands between racks.
Run the arithmetic before you trust a quote. A 150W LED high bay light at 200 lm/W produces 30,000 lumens. Apply a maintenance factor of 0.8 and a utilisation of 0.6, and about 14,400 lumens reach the work plane. Spread over 100 m², that is 144 lux average. To reach 200 lux, you need one fixture per 70 m², not one per 100.
Ask for IES files and a Dialux or Relux report with your own aisle dimensions. A supplier who cannot produce an IES file is estimating, usually against a flat empty floor.
Glare, UGR and the Forklift Driver
UGR 25 is the usual ceiling for storage areas, and high bays break it easily. At 9 m, a wide lens sits close to the driver's line of sight for anyone 15 to 20 m down the aisle. The fix is optical, not wattage: a recessed lens, a shielding ring, or a narrower beam aimed at the rack.
Colour matters for picking. 4000K with CRI 80 or better keeps red and orange labels distinguishable, where 5700K washes them out. Flicker matters for handheld scanners and cameras; ask for percent flicker under 8%, not just "flicker free".
Dust is the slow killer. In a feed mill or foundry, a 1 mm layer on the lens and heat sink cuts output and raises driver temperature. An IP65 LED high bay light with a flat lens cleans in one wipe. A finned housing open to the ceiling void does not.
Quick Answers
How many fixtures for 1,000 m²? At 200 lux and 70 m² per fixture, fourteen. At 150 lux, ten.
Is a 150W LED high bay light enough at 12 m? Yes, with 60° optics and 8 to 9 m spacing. The wattage is not the question; the spacing and optic are.
90° or 120°? 90° for rack aisles between 6 and 12 m. 120° below 6 m, or where the floor is open and no rack shadows the beam.
Do I need the emergency version? If the aisle is an escape route, yes. Self-contained three-hour units exist, and the battery ages first in a hot roof void.
Will a five-year warranty cover the driver? Only if the terms say so. Ask for the ambient temperature limit in writing, because a 50°C ceiling voids many standard warranties.
Before You Order
Put these on an LED high bay light specification sheet, in this order, before you ask for a price:
- Target vertical lux on the rack face, and the height of the top picking level
- Mounting height, aisle width and rack depth
- Beam angle and whether asymmetric optics are allowed
- UGR limit, CCT and CRI
- Maintenance factor and the IES file for the exact model
- IP rating, ambient temperature and cleaning method
- Emergency requirement and battery test interval
- Warranty terms covering the driver, not only the LED module
Send that sheet with a racking drawing, and quotes become comparable. Without it, three suppliers will price three different lighting designs and call them the same product.
You can check wattages, beam options and driver brands in our LED high bay light range, or browse the full product catalog for linear and flood alternatives over open areas. If you have a racking layout, send it through our inquiry page and we will run the vertical illuminance check before quoting. For projects above 10 m or with mixed rack heights, contact our engineers before you order, because the optic choice is fixed at order time and cannot be corrected on site.
