40 lux corresponds to 40 lumens per square meter when the illuminated area is exactly 1 square meter. To convert 40 lux into lumens, you multiply by the area in square meters, so if the area is 1 m², 40 lux equals 40 lumens.
Lux measures illuminance, which is lumens spread over an area. Lumens indicate total light output, while lux tells how bright that light appears on a surface. Therefore, converting lux to lumens requires knowledge of the surface area illuminated.
Conversion Tool
Result in lumens:
Conversion Formula
The conversion from lux to lumens depends on the area over which the light is spread. The formula is:
Lumens (lm) = Lux (lx) × Area (m²)
This formula works because lux measures lumens per square meter. If you know the illuminance in lux and the area in square meters, multiplying them gives the total luminous flux in lumens.
For example, if an area of 2 square meters is lit with 40 lux, then:
- Lumens = 40 lx × 2 m² = 80 lm
This means 80 lumens of light are spread over that 2 m² area, creating an illuminance of 40 lux.
Conversion Example
- Convert 25 lux to lumens over 3 m²:
- Start with the formula: Lumens = Lux × Area
- Calculate: 25 lx × 3 m² = 75 lumens
- Result: 75 lumens of light illuminates the 3 m² space
- Convert 50 lux to lumens over 0.5 m²:
- Formula applies similarly
- 50 lx × 0.5 m² = 25 lumens
- The total luminous flux is 25 lumens
- Convert 60 lux to lumens over 4 m²:
- Multiply lux by area
- 60 × 4 = 240 lumens
- 240 lumens spread over 4 square meters
- Convert 35 lux to lumens over 1.2 m²:
- Lumens = 35 × 1.2 = 42 lumens
- This means 42 lumens illuminate 1.2 m²
- Convert 45 lux to lumens over 2.5 m²:
- Calculate 45 × 2.5 = 112.5 lumens
- The light output is 112.5 lumens for that area
Conversion Chart
| Lux (lx) | Lumens (lm) for 1 m² |
|---|---|
| 15.0 | 15.0 |
| 20.0 | 20.0 |
| 25.0 | 25.0 |
| 30.0 | 30.0 |
| 35.0 | 35.0 |
| 40.0 | 40.0 |
| 45.0 | 45.0 |
| 50.0 | 50.0 |
| 55.0 | 55.0 |
| 60.0 | 60.0 |
| 65.0 | 65.0 |
This chart shows lux values from 15 to 65 and their equivalent lumens assuming a 1 square meter area. To use the chart for different areas, multiply the lumens by the area in square meters.
Related Conversion Questions
- How many lumens are in 40 lux across 2 square meters?
- What is the formula to convert 40 lux to lumens when area changes?
- Can I find lumens from 40 lux without knowing the area?
- How does the size of the area affect converting 40 lux to lumens?
- What lumens correspond to 40 lux on a 5 m² surface?
- Is 40 lux equal to 40 lumens always?
- How to calculate lumens if I have 40 lux and an irregularly shaped area?
Conversion Definitions
Lux: Lux is a unit measuring illuminance, which tells how much light falls on a surface per square meter. It quantifies the perceived brightness that a human eye would see on that surface, taking into account the total luminous flux spread over an area.
Lumens: Lumens measure the total amount of visible light emitted by a source. It indicates the luminous flux, or the quantity of light energy perceived by the human eye, regardless of the area it covers or how it spreads.
Conversion FAQs
Why do I need to know the area to convert lux to lumens?
Because lux measures illuminance (lumens per square meter), the area is essential. Without the surface size, you can’t determine total light output in lumens. For example, 40 lux over 1 m² equals 40 lumens, but over 2 m² it’s 80 lumens. The area changes the total luminous flux.
Can I convert lumens to lux without knowing the area?
No, converting lumens to lux requires the surface area that the light illuminates. Lux is lumens divided by area, so missing the area means you can’t find the illuminance. You need both total light and area to convert between these units.
Does the shape of the illuminated surface affect the conversion?
The shape itself doesn’t change the formula, only the total area matters. Whether the light covers a rectangle, circle, or irregular shape, you multiply lux by the total surface area in square meters to get lumens. Accurate area measurements are important for precise conversion.
Is the conversion accurate if the light source is not uniform?
If the illuminance isn’t uniform over the area, simple multiplication will only give an approximation. Lux is an average value, so areas with uneven lighting require measuring lux at different points and calculating a weighted average before converting to lumens.
Why does 40 lux equal 40 lumens only at 1 square meter?
Because lux equals lumens per square meter, 40 lux means 40 lumens spread evenly over one square meter. If the area changes, the total lumens must be recalculated by multiplying lux by the new area, so the equality holds only at 1 m².