Lumens (lm) and watts (W) measure two different things: lumens measure the amount of light, watts measure energy use. In the LED era you can no longer judge brightness by watts — look at lumens.

The difference

  • Lumen (lm) — the higher the number, the brighter the light.
  • Watt (W) — the lower the number, the less electricity the lamp draws.

Brightness used to be linked to watts because incandescent lamps were all about equally efficient. LED produces the same light at a fraction of the power, so watts say nothing about brightness any more. Rough conversion: old lamp watts × 10 ≈ lumens.

Old lamp~LumensLED power
40 W~470 lm5–6 W
60 W~800 lm7–9 W
75 W~1100 lm10–12 W
100 W~1600 lm13–16 W

How many lumens does a room need?

The formula is simple: lumens needed = floor area (m²) × recommended lm/m².

RoomRecommended level
Bedroom150–200 lm/m²
Living room200–300 lm/m²
Kitchen, ambient250–350 lm/m²
Kitchen worktop500+ lm/m²
Bathroom300–500 lm/m²
Home office, desk300–500 lm/m²
Hallway, utility room100–150 lm/m²

Example: a 20 m² living room × 250 lm/m² = ~5000 lumens. Spread that across several fittings (ambient plus task light) rather than one lamp.

What else to consider

  • Dark surfaces absorb light — add 20–30 %.
  • High ceilings need more output.
  • Colour temperature does not affect brightness: how to choose it.
  • Light is best distributed in layers: lighting layout.

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What is the difference between lumens and watts?

Lumens measure the amount of light; watts measure energy consumption.

How many lumens per square metre do I need?

It depends on the room: 150–250 for bedrooms and living rooms, 300–500 for kitchens and bathrooms.

How do I calculate the lumens I need?

Multiply the floor area in m² by the recommended lm/m² for that room.

How many lumens does an old 60 W bulb give?

Roughly 700–800 lumens.

How do I convert watts to lumens?

As a rough rule, multiply the old incandescent wattage by ten.

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