Most under-shelf LED bars on the market ship with a 120° beam angle — wide, soft, and forgiving. It's the safe default. But for category lighting on a deep retail gondola, a narrower 90° optic frequently produces a better shopper experience and measurable category lift. This article explains the physics and the decision.

The geometry: 120° vs 90° on a 600 mm shelf

Take a typical retail gondola: 600 mm shelf depth, 350 mm vertical clearance to the shelf below, LED bar mounted along the front lip. The beam from the bar has to travel the full 600 mm to illuminate products at the rear of the shelf — and it has to do this without spilling so much light past the shelf edge that the aisle becomes glary.

A 120° beam (the default for most under-shelf LED) spreads light across roughly 1.5 metres at a 350 mm distance. About 40% of that flux falls inside the shelf footprint; the rest spills forwards into the aisle and downwards onto the shelf below. Visually, the front edge of products is bright; the rear of the shelf is noticeably dimmer; the aisle picks up scatter that can read as glare to a shopper at standing height.

A 90° beam spreads light across roughly 1 metre at the same distance. Closer to 75% of the flux lands inside the shelf footprint. The light reaches the rear of the shelf with workable intensity; the aisle stays cleaner; the shelf below is less affected by scatter.

"Wide beam optics deliver less light to the back of the shelf. For deep retail categories, that's where the products you want shoppers to find tend to live."

Why this matters for category sales

Retailers measure shelf engagement in dwell time and pick-up rate — how long a shopper stops at a section, and how often they actually take something off the shelf. Both metrics are sensitive to whether the shopper can read product names and labels at the rear of the shelf, where back-stock and lower-velocity SKUs typically sit.

A category lit with 120° optics shows a measurable falloff in pick-up rate for SKUs in the rear third of the shelf. With 90° optics, the falloff is significantly reduced — back-shelf products read more clearly, get evaluated more often, and convert at rates closer to front-shelf products. The visual difference isn't subtle; if you stand in front of a shelf lit both ways, the back-of-shelf gradient is immediately obvious.

When 120° is still the right choice

Wide-beam under-shelf LED isn't wrong everywhere. It's the right answer when:

  • Shallow shelves (≤ 400 mm deep) where the rear is naturally close to the light source.
  • Display shelves rather than category shelves — single-product face-out merchandising where every product is at the front edge.
  • Cool-cabinet interior lighting where the goal is overall brightness, not focused throw.
  • Budget projects where the wider-beam product is significantly cheaper and the depth penalty is acceptable.

When 90° wins clearly

  • Deep gondola shelving (550–700 mm) — the standard supermarket and hypermarket format.
  • Category-rich aisles where back-shelf SKUs need to read clearly — packaged foods, beverages, snacks, dry goods.
  • Premium retail formats where lighting consistency across the shelf face is part of the brand standard.
  • Aisles with sensitive sight-lines — where wide-beam scatter into the aisle would create glare for shoppers at standing height.

Specification reference

The CAPST SFT series ships with a narrow 90° optical lens specifically for deep-shelf throw. The wider-beam SNK series at 120° is the right call for shallower shelves, refrigerated cabinets, and applications where uniform coverage matters more than back-shelf reach. Both run on the same 24V DC platform, so a project can mix the two without changing the power architecture.

How to test before committing to a full rollout

Before specifying an entire store's worth of one optic, set up a controlled test on two adjacent gondola sections — same product mix, same store, same aisle. Run 90° on one and 120° on the other for two weeks. Pull the SKU-level sales data afterwards and compare. The result is usually clear; if it isn't, you've answered the question for this particular category and can default to the cheaper option without regret.

If you're planning a category-lighting upgrade and want to talk through the right optic for your shelf depth and product mix, the technical pack for SFT and SNK includes the photometric files (IES) needed to model the scene properly in DIALux or Relux. Request both packs through the contact form and our team will help interpret the output for your specific gondola dimensions.