Lumens to Lux Calculator

Direction

Luminous flux, lm

Area, m²

Result

Illuminance, lx66.67
Luminous flux, lm1,000
LED wattage, W10
Incandescent wattage, W83.3
For comparisonкак в коридоре
Area, m²15

Lumens describe the lamp, lux describe the surface

Converts luminous flux into illuminance over an area and back, and shows the LED and incandescent wattage that would produce it.

Lumens are a property of the lamp: how much light it puts out in total. Lux are a property of the place: how much of that lands on a square metre. The same lamp gives plenty of lux in a cupboard and very few in a hall — same output, different area.

Which is why comparing lamps by wattage is meaningless. Watts describe consumption, not brightness: a 10 watt LED matches a 75 watt filament lamp because it makes about a hundred lumens per watt against twelve.

What this calculator shows

Illuminance in lux, or the luminous flux needed to reach it
The LED and incandescent wattage that would deliver that flux
What the resulting light level feels comparable to

What to keep in mind

Assumes light spread evenly across the area; a real fitting throws a pool and the edges of the room will be darker.
Efficacy is taken as 100 lm/W for LED and 12 for incandescent — typical figures for domestic lamps.

FAQs

How many lumens per watt?

80 to 120 for LED, about 60 for fluorescent, 20 for halogen, 12 to 15 for incandescent. That is why a 10 watt LED replaces a 75 watt bulb.

How many lux does a room need?

A hundred in a bedroom or corridor, 150 in a living room, 300 in a kitchen, 500 in a study, 750 in a workshop. The figures come from workplace lighting standards.

Why does it look dimmer than the calculation says?

The calculation ignores reflection and shades. Dark walls and ceiling swallow up to a third of the light and a dense shade another third; in such rooms add 30 to 50 percent.

How do lux differ from candelas?

A candela measures intensity in one direction, a lux measures illuminance on a surface. Torches are described in candelas, rooms in lux, lamps in lumens.

Worked example

One lamp in a room

Input: 1,000 lm over 15 m²

Output: 66.7 lux — corridor level

Note: A living room wants around 150 lux, so 2,250 lumens. One 1,000 lumen lamp will not do it; three is the minimum.

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Lumens to Lux Calculator

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