Understanding LRV Requirements for TGSI Compliance in Australia

The Decision You're Making

Before specifying a TGSI or stair nosing colour, you are answering one question: will this element remain visually detectable to a person with low vision, against the actual substrate, on the actual installation day, in the lighting conditions that actually exist, and will it remain detectable in five years? Everything else (brass vs stainless, yellow vs charcoal, matte vs gloss) follows from that answer.

Luminance contrast is the measurable proxy for detectability. Get it right at specification stage and the project passes audit. Get it wrong and remediation costs (re-supply, re-install, re-inspect) start compounding.

What LRV Actually Measures

Light Reflectance Value (LRV) is the proportion of visible light a surface reflects under standard illumination, expressed on a scale from 0 (absolute black) to 100 (perfect white). A single LRV reading tells you nothing about compliance. What matters is the difference between two LRVs, the TGSI and the surface it sits in, and how that difference is calculated.

The Australian standard for that calculation is the Bowman-Sapolinski equation, cited in Appendix E of AS/NZS 1428.4.1:2009 and Appendix B of AS 1428.1:2021:

The simpler Weber ratio, [(B1 − B2) / B1] × 100, looks similar but is a different equation entirely and is not accepted by Australian access consultants. If a supplier quotes contrast using the Weber form and labels it Bowman-Sapolinski, ask for the test report.

The Three Compliance Thresholds

AS/NZS 1428.4.1:2009 defines three TGSI construction categories, each with its own minimum luminance contrast against the surrounding surface:

• Integrated TGSI: 30% minimum (clause 2.2.1). A single unit where the dome array and the surrounding base plate are the same material and colour: the base reinforces the visual signal, so less contrast is required. Example: Kahn® Porcelain paver; Renzo® Tile.
• Discrete TGSI: 45% minimum (clause 2.2.2). Individual studs installed directly into the substrate with uniform luminance across the dome, with no integrated base. The stud stands alone against the floor, so more contrast is needed for detection. Example: Nouvel® Classic.
• Composite discrete TGSI: 60% minimum (clause 2.2.3). Discrete studs where the sloping sides and the upper surface have different colours, e.g. a stainless stud with a contrasting carborundum top. The highest threshold because the eye can lock onto just the top, which is a smaller visible element. Example: Nouvel® CarbTop.

For stair nosings (AS 1428.1:2021 clause 11.1), the threshold is 30% against the adjacent tread, over a contrast strip 50-75mm deep.

Why This Trips Specifiers Up

Five common traps, in the order they bite:

1. Specifying colour instead of LRV. "Yellow TGSIs on cream limestone" can deliver anywhere from 12% to 55% contrast depending on which yellow and which limestone. Always request the measured LRV of both the TGSI and the substrate; always run the Bowman-Sapolinski calculation.
2. Dividing by the wrong surface. Always use Y₂ = lighter and Y₁ = darker. Hitting 60% against a dark substrate (LRV 10) requires a TGSI with LRV above 45. Hitting 60% against a light substrate (LRV 60) requires a TGSI below LRV 10. The same percentage is a very different design problem depending on which surface is the floor.
3. Testing the sample, not the install. LRV should be measured on the finished, sealed, installed surface. Sealers, polishes, grout and mortar all shift LRV. The showroom tile is not the slab on site.
4. Ignoring LRV drift over time. Brass patinates and loses 25-35 LRV points over 5-10 years. Polymer UV-fades 5-15 points over 3-5 years outdoor. Stainless, porcelain and natural stone are essentially stable. If you specify a drifting material at the exact regulatory minimum, the project will fail its first post-handover audit.
5. Missing the wet-condition requirement. Outdoor TGSIs must meet the contrast threshold both wet and dry. Appendix E applies the same threshold to both conditions: there is no reduction factor for wet. A product that passes dry on new concrete but fails wet is non-compliant.

Design With Margin

Access consultants almost universally recommend specifying 5 percentage points above the regulatory minimum: 35% where 30% is required, 50% where 45%, 65% where 60%. That margin absorbs substrate variation, patina, fade, and the real-world gap between the laboratory LRV and the installed-and-sealed LRV.

The cost of margin at specification is effectively zero. The cost of remediation after handover (removing, re-supplying, and re-installing non-compliant TGSIs) is where projects lose money and reputation. Specifying the bare minimum is optimising for the wrong thing.

The Practical Specification Workflow

1. Measure the substrate. If the floor is stone, terrazzo or polished concrete, take readings from three locations on site or at least three production samples, not one tile from a showroom.
2. Select the TGSI material with a target contrast of minimum + 5pp. For integrated tactiles, target 35%; for discrete, 50%; for composite discrete, 65%.
3. Verify with Bowman-Sapolinski. Run the numbers for both installed-day LRV and, where the TGSI material drifts, end-of-warranty LRV. Both must clear the threshold.
4. Test on the installed surface. A handheld colorimeter on the sealed, installed floor is the definitive reading. Keep the certificate with the O&M pack.
5. Re-test after any substrate change. Re-sealing, re-polishing, re-tiling, or even a deep clean with new chemistry can shift the substrate LRV enough to push contrast below the threshold. Re-test after any works.

How Korb Makes This Easier

Korb publishes measured LRV data for every TGSI product: not just the dome colour, but the composite reading with the carborundum top where applicable. That means the Bowman-Sapolinski calculation can be run at specification stage, against whatever substrate LRV the architect has, without waiting for physical samples.

For projects where the substrate is uncertain or variable (polished concrete pours, mixed stone, retrofits onto unknown existing floors) Nouvel® CarbTop delivers reliable high contrast (composite discrete, 60%+) against the broadest range of Australian floor finishes. Where through-body colour is required for 20-year LRV stability, Kahn® Porcelain and Renzo® Vanguard (composite FRP) remove the drift problem entirely.