The same downlight casts very different light onto a matte grey wall vs a satin white one. LRV (Light Reflectance Value) is the spec line designers miss, and the one that makes the most difference at handover.
Four ideas to carry into the next specification conversation you have.
LRV 80 reflects about 80% of the visible light that lands on it, LRV 5 about 5%. It is measured to a published method (BS 8493), not judged from a colour card. The 30-point LRV rule you may have met is accessibility guidance on visual contrast between surfaces, not a rule about interreflection.
Matt scatters close to a diffuse lobe and gives an even ambient. Gloss returns the same energy into a narrow specular lobe, so you see the luminaire in the wall. LRV tells you how much visible light the surface returns; gloss tells you how that return is distributed. Specify both: gloss units at a stated angle per ISO 2813, alongside the LRV.
The maintained illuminance a task needs is set by the task, so paint never lowers the requirement. Bright walls can reduce the installed power required to achieve the same target illuminance, by raising the utilisation factor. Dark accent walls buy their look with watts.
Write 'wall: LRV ≥ 70' alongside the paint code. Without it, the contractor is free to substitute and your DIALux model breaks.
Indicative Light Reflectance Value bands for common interior finishes. Bands vary by product, batch, substrate and number of coats, so specify a measured value on the delivered product rather than a value from this table.
| Finish | LRV | Against the standard’s ranges |
|---|---|---|
| White matt paint | 80-85 | Top of the ceiling range, top of the wall range |
| Off-white matt | 70-75 | Inside the ceiling range, inside the wall range |
| Cream / beige matt | 55-65 | Inside the wall range, below the ceiling range |
| Light grey matt | 40-50 | At or below the bottom of the wall range |
| Medium grey matt | 25-35 | Below the wall range; a deliberate choice to justify |
| Dark grey / charcoal | 10-15 | Well below every wall and ceiling range |
| Walnut wood veneer | 10-20 | Well below the wall range; verify the actual veneer |
| Polished marble (light) | 60-70 (gloss) | Reflectance is only half the story: check reflected glare |
Five points the finishes consultant and the lighting consultant should agree on early.
A significant share of the light reaching a desk has already struck a ceiling, a wall or the floor. Lower the ceiling and wall reflectances and the same luminaires deliver less on the task. The size of that loss is an output of the calculation for that room, that distribution and those surfaces, not a constant, so run it rather than quote a percentage.
A gloss white and a matt white can carry a similar LRV and still behave completely differently, because gloss returns the light into a narrow specular lobe: where angle in equals angle out, the observer sees the luminaire itself in the wall. That is reflected glare and veiling reflections, which are treated separately from luminaire glare; UGR (CIE 117) rates discomfort from the luminaires in the field of view and its tabular method does not model specular reflection off room surfaces. Specify matt or eggshell on large vertical surfaces, especially near screens, and keep gloss for trim.
Carpet commonly reads far darker than the sample looked, and floors sit at the bottom of the recommended reflectance range to begin with. Where light on faces matters, a lighter floor finish is a design lever, not a decorator’s choice. Treat any LRV band you have been quoted as indicative and ask for a measured value on the specified product.
The reflectance a painted gypsum ceiling actually delivers depends on the paint, its sheen, the substrate and how many coats it received. A ceiling handed over a coat short, or in a different sheen from the approved sample, is a lighting change that nobody logged as one. Inspect and, where it matters, measure at commissioning.
The lighting model must be reviewed whenever repainting materially changes surface reflectance, sheen, or another modelled property. Document the LRV assumption in the O&M manual so future tenants understand the trade-off they are making.
NLC finishes its own luminaire bodies in-house, so the finish on the luminaire is a controlled input to your project rather than whatever arrived in the crate. For any surface that feeds the calculation, ask for a measured value against a stated method.
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