This week in the UK, the light changed. Two clear days after months of grey - and suddenly children were back on bikes, people lingered outside, parks felt alive. Nothing structural changed. Just the light. And the mood lifted. Light does that. We know this physically. Natural light, greenery, even a view from a window - it changes how we heal, sleep, focus, cope. A windowless corridor isn’t neutral. The body knows the difference. But there’s another kind of light that matter