What do lumens, kelvin and watt equivalent mean on a light bulb box?
They describe three separate things, and only one of them is brightness. The confusion comes from decades of buying bulbs by wattage, which no longer works.
Lumens measure brightness — the actual light output. This is the number to buy by. Rough guide: 400–500 lumens suits a small lamp, 800 lumens is the standard main bulb, 1,500+ suits a kitchen or a large room. More lumens means more light, regardless of technology.
Watts measure power consumption, not brightness. With incandescent bulbs the two tracked each other closely enough that everyone used watts as shorthand for brightness. LEDs broke that relationship — an LED producing 800 lumens draws about 8–10W, where the old bulb drew 60W. "60W equivalent" on an LED box means "about as bright as the 60W bulb you remember", not that it uses 60W. It exists purely as a translation for people who still think in the old units.
Kelvin measures colour temperature — whether the light is warm or cool. Confusingly, lower numbers are warmer:
- 2,700K — warm white, the colour of an old incandescent bulb. Living rooms, bedrooms.
- 3,000K — soft white, slightly crisper. Kitchens, bathrooms.
- 4,000K — neutral or cool white. Garages, offices, workshops.
- 5,000–6,500K — daylight, distinctly blue-white. Task lighting, but harsh in a living room.
Mixing colour temperatures in one room looks wrong, so keep them consistent.
Two more things worth checking on the box: CRI (colour rendering index), where 90+ makes colours look natural and matters in kitchens and bathrooms; and whether the bulb is dimmable, since a non-dimmable LED on a dimmer circuit flickers, buzzes and fails early.