Blog

We metered a 32m grocery aisle last year: 900 lux on the floor, 280 lux on the second shelf where the barcode sits. The owner asked for higher wattage. The fix was a narrower beam. Wattage sets the energy bill; beam angle sets whether lumens land on the product face or on the floor. This is the same check we run in Dialux before any retrofit leaves our factory — including the DIA Group and Carrefour store retrofits we have delivered without reopening ceilings.

1. Why floors lie: vertical lux is the buying metric

EN 12464-1 lists a sales area at 300 lux with UGR 22, but supermarket gondolas are specified at 500 to 750 lux vertical on the product face — measured at 0.8 to 1.2m height, not at the 0.85m horizontal workplane. TRILUX’s EN 12464-1 explainer makes the split explicit: photometric requirements for the sales area exceed the bare occupational minimum and must be verified per task area (TRILUX: EN 12464-1 Light and Safety at Work). For maintained levels in retail, the IES Recommended Light Levels table is the independent reference (IES Recommended Light Levels (PDF)), and vertical illuminance at 5 ft (1.52m) is the practical retail check quoted by U.S. retail practice at 30–50 fc (Hyperlite: Vertical vs Horizontal Lighting in Retail Rows).

A 30W 60° and a 30W 15° deliver identical lumens; at 3.5m one paints a 4.0m circle, the other a 0.9m pool. The circle wastes half its lumens between bays; the pool holds the face at uniformity 0.8 but needs tighter spacing. Choosing wattage without angle is why half the retrofits we audit meter bright floors and dark labels.

2. The 15° to 60° rule at 3.0–3.5m

We use this table for every aisle at 3.0 to 3.5m rail height. Pool diameter = 2 × height × tan(beam/2); all diameters below at 3.5m, assuming ~3,000–4,500 lm per head at Ra 90.

If you can see the scallop on the shelf edge, spacing is 0.5m too wide. For Dialux practice, vertical illuminance at the shelf face and uniformity U0 = Emin/Ē are the two checks to hold — see the community walkthrough on vertical illuminance in Dialux (DIALux: Vertical Illuminance tutorial).

3. Spacing that holds uniformity on the face, not the floor

Floor uniformity U0 0.4 is easy; shelf-face uniformity 0.7 is the line that decides sell-through. At 3.5m with 36° heads, spacing 3.0m holds vertical shelf lux at ~620 lux ±18% across a 1.2m bay; at 4.0m it drops to ±38% and the second shelf reads dark. For narrow 15° hero bays, overlap pools by ~30% so the hot spot lands on the hero, not between heroes.

Where one rail must serve two gondolas, a dual-panel head with independently tiltable panels replaces two single-head runs and cuts track length per aisle by up to 50%. For a full spacing table for 15° to 90° at 3.0–3.5m and the two-step Dialux check we use before quoting DIA retrofits, see this LED linear light range for supermarket aisles with Dialux-verified layouts — the table is the same one we issue with every quotation.

4. Two-step Dialux verification we run before quoting

Experience note: Every aisle is simulated before it is quoted — optical design and Dialux run before tooling, 24-hour aging per batch. That is how we keep the “no reopening ceilings” promise for live-store retrofits.

1. Shelf lux at 0.8m: model gondola faces as vertical calculation surfaces at 0.8m, 1.2m and 1.6m. Target 500–750 lux, U0 ≥0.7. Adjust beam and spacing, not wattage, until the middle shelf stops dipping.

2. Glare at 1.2m: check Unified Glare Rating at 1.2m shopper eye height along the aisle centre line. Hold UGR <22 for supermarket aisles, <19 for boutique cross-aisles per EN 12464-1. If UGR spikes, narrow the beam or add a honeycomb — do not dim the whole aisle.

5. Fresh food adds a second filter: R9

For meat and produce, beam without spectrum still fails. CRI Ra averages eight pastels with no saturated red; a Ra 90 source can still be R9 25 and make beef read brown. Meat counters need Ra 90 plus R9 ≥50 (premium R9 80+), and TM-30 Rf/Rg tells the rest. FreshFocus and Promolux publish the same split — we keep the aisle table above unchanged and swap the source spectrum per counter. Ecocore readers running chilled cases can keep the same 36° geometry and change only the source.

Beam angle moves lux from floor to face without adding fittings — spacing holds uniformity, Dialux proves glare before ceilings are opened. Wattage follows lux, not the other way around.