LRV stands for Light Reflectance Value — a number from 0 to 100 telling you how much visible light a colour reflects. Pure black sits at 0 (absorbs everything), pure white at 100 (reflects everything). Nothing real hits either extreme, so most paints land somewhere in between.
Why should you care? Because LRV is the single best predictor of how a colour will actually behave on your walls. Two greys can look near-identical on a chart but feel completely different once they're up — one bounces light around a dim hallway, the other swallows it whole. The number cuts through the guesswork.
As a rough guide: anything above about LRV 70 reads as a genuine light colour and lifts a dark room. Sit in the 40s–50s and you've got proper mid-tones — characterful but they'll eat some light. Below 20 and you're into dramatic, light-absorbing territory that wants good natural light or clever artificial lighting to sing.
North-facing rooms are where this really bites. They get cool, indirect light, so a colour with a low LRV can feel gloomy and flat. That's why something like Farrow & Ball Cornforth White or Little Greene Loft White earns its keep up north — decent reflectance keeps things feeling open. For a south-facing room drenched in light, you can happily drop the LRV and go richer — Farrow & Ball Hague Blue or Studio Green will look sumptuous rather than dingy.
The "but what about" question I always get: does a high LRV mean a colour is *pale*? Not quite. LRV measures lightness, not saturation, so a soft warm white and a chalky grey can share a similar value while looking nothing alike. Use LRV to judge weight, use your eyes and a tester to judge undertone.
Practical advice: check the LRV on the brand's datasheet before you commit, match it against which way your room faces, then test in situ across the day. A £6 sample pot beats a repaint every time.