Lumens vs watts: how to buy LED bulbs that actually look right

For a hundred years a bulb's brightness was its wattage, because every bulb was an incandescent and they all converted power to light at the same poor rate. LEDs broke that. A 10 W LED can be brighter than a 60 W incandescent. So the packaging moved to lumens, and added two more numbers that matter more than most people realise.

Lumens

Brightness. Roughly: 450 lumens is the old 40 W; 800 is 60 W; 1100 is 75 W; 1600 is 100 W. A living room wants 1,500 to 3,000 lumens total across all its lights; a kitchen more. "Equivalent to 60 W" on a box is a lumen figure in disguise; check the actual number.

Colour temperature

Measured in kelvin. 2700 K is warm white, the colour of a traditional bulb, right for living rooms and bedrooms. 3000 K is slightly crisper. 4000 K is neutral white, for kitchens, bathrooms and work. 5000 to 6500 K is daylight and reads as cold indoors. Mixing temperatures in one room looks wrong; buy the same for a room.

CRI

Colour rendering index, on a scale to 100. It's how accurately the light shows colours. Cheap LEDs sit at 80 and make skin greyish and food dull. 90 or above looks right. The number is often missing from budget packaging, which tells you something.

Dimmable

Must be stated. A non-dimmable LED on a dimmer switch flickers, buzzes and dies early. And LED dimmables need an LED-compatible dimmer; old resistive dimmers don't work properly with them.

Lifespan

Quoted in hours: 15,000 is decent, 25,000 is good. At three hours a day that's 14 to 23 years. A bulb with no stated lifespan probably doesn't have one worth stating.

Buying

Packs of four or ten are cheaper per bulb, but only if you need them. Philips, Osram and Integral are reliable; own-brand from a specialist lighting retailer is usually fine; unbranded marketplace bulbs are where the flicker and early failures live.