LRV stands for Light Reflectance Value — a number from 0 (theoretical pure black) to 100 (pure white) that tells you how much visible light a colour reflects back into the room. It's the single most useful number on a paint card, and most decorators ignore it.
Here's how to use it. Work out how much natural light your room gets, then pick an LRV to suit. A dark, north-facing room that never sees direct sun needs a colour that earns its keep on light — generally LRV 50 and up, ideally into the 70s. A bright, south-facing room can take a much lower LRV without feeling like a cave, because there's plenty of light for the colour to play with.
A few practical numbers to hold in your head: anything above about LRV 70 reads as a genuine "light" colour. The 50–70 band is light-with-presence — soft greys and muddy off-whites that still lift a room. From 20 to 50 you're into proper mid-tones. Below 20 is depth-and-drama territory, and below 10 is near-black.
For a dim room crying out for light, Farrow & Ball Pointing is a reliable high-LRV choice that doesn't go cold and clinical, and Strong White does the same job on the cooler side. Step down a touch and Skimming Stone or Cornforth White give you a warmer mid-light grey. When you actively want to lean into a dark room rather than fight it, go the other way entirely — Hague Blue or Studio Green wrap a space up beautifully, and the low LRV is the point, not the problem.
The "but what about" question I always get: does a high LRV guarantee a room feels bright? No. LRV measures reflectance, not undertone or chroma. A grey with a cool blue base at LRV 65 can still feel flat and chilly in poor light. LRV tells you *how much* light comes back, not *what colour* it'll look once it gets there.
So treat LRV as your first filter, not your final answer. Shortlist on the number, then get the actual colour up on big boards — both ends of the room, morning and evening. The card never tells the whole story.