Warm light, measured properly

Two numbers on a bulb box determine whether your evening feels like an evening, and most people read neither. Kelvin measures colour: 2700K is the warm amber of the old incandescent bulb, 4000K is an office corridor, 6500K is a dental surgery at noon. Lumens measure quantity: 400 is a generous reading lamp, 800 the old sixty-watt standard. Watts, the number everyone still asks for, now measures only electricity. The manufacturers print all of this on the packet. The packet, admittedly, does not make it easy.

The home rules are short. Nothing over 2700K in any room you use after dark; 2200K — sold as flame or extra warm — earns its place in the lamps that burn latest. Do not fear low lumens: three lamps of 400 make a far better room than one bulb of 1200, because distribution beats output everywhere except over a workbench. Check for a CRI of 90 or above, the quiet number that decides whether wool, wood and skin show their real colours. And buy dimmable, but only if the dimmer actually exists.

One warning saves the whole project: dim-to-warm and dimmable are different claims. An ordinary dimmable LED at ten percent gives you less of the same cold light; a dim-to-warm bulb slides down toward 1800K as it dims, the way a filament did, and it is the one worth searching the shelf for. Take five minutes with the boxes and the whole exercise costs nothing extra — warm bulbs are priced like cold ones. The light in your home is set by numbers someone already printed. Read them once, and buy the evening you actually want.