Lumen (lm) to Lux (lx) Calculator
Use this tool to convert total luminous flux in lumens into illuminance in lux based on the lit area.
If you are planning room lighting, office fixtures, workshop lamps, or even photography setups, converting lm to lux helps you understand how bright a surface will actually look. Lumens describe the total light output from a source, while lux tells you how much of that light reaches a given area.
What is the difference between lumens and lux?
People often mix these terms up, but they measure different things:
- Lumen (lm) = total amount of visible light emitted by a lamp.
- Lux (lx) = light intensity over a surface area.
In simple terms: lumens are what the bulb produces; lux is what your desk, floor, or wall receives.
lm to lux formula
The conversion is straightforward:
Lux = Lumens ÷ Area (m²)
If your area is entered in square feet, first convert to square meters:
1 ft² = 0.092903 m²
That is exactly what the calculator above does automatically.
How to use this calculator
- Enter the lamp output in lumens.
- Enter the size of the area being illuminated.
- Select m² or ft².
- Click Calculate Lux.
The result also includes approximate foot-candles (fc), which are commonly used in U.S. lighting specs.
Worked examples
Example 1: Small room
A 1,500 lm fixture lights a 15 m² room.
Lux = 1500 ÷ 15 = 100 lx
This is acceptable for hallways or basic ambient lighting, but likely too dim for detailed tasks.
Example 2: Desk task lighting
You have an 800 lm desk light spread over 1.6 m².
Lux = 800 ÷ 1.6 = 500 lx
About 500 lx is a common target for reading and office desk work.
Example 3: Using square feet
Suppose a 2,000 lm light covers 120 ft²:
- Area in m² = 120 × 0.092903 = 11.148 m²
- Lux = 2000 ÷ 11.148 ≈ 179.4 lx
Recommended lux levels (typical ranges)
| Space / Activity | Recommended Lux |
|---|---|
| Hallways / storage | 50–100 lx |
| Living room ambient | 100–300 lx |
| Kitchen general | 300–500 lx |
| Office desk / reading | 300–750 lx |
| Workshop / precision tasks | 750–1,500 lx |
Important real-world notes
The basic lm to lux formula is perfect for quick estimates, but real installations can vary due to:
- Ceiling height and fixture placement
- Beam angle (spot vs flood lighting)
- Wall and surface reflectivity
- Diffusers, shades, and lens losses
- Lamp aging and dirt accumulation
So treat this as a planning tool, then verify with a lux meter for critical environments.
Quick lux planning tips
- Layer light: combine ambient, task, and accent sources.
- Prioritize lux where tasks happen (desk, counter, bench).
- Use dimmers so you can tune brightness for comfort and time of day.
- Don’t compare bulbs by watts—compare by lumens.
FAQ
Can I convert lux back to lumens?
Yes. Rearranging the same equation gives: Lumens = Lux × Area (m²).
Is lux the same as brightness perception?
Not exactly. Lux is a physical measurement. Human perception also depends on contrast, color temperature, and adaptation.
Why does my room still feel dark even if lux is “enough”?
You may have uneven distribution, shadows, dark wall colors, or too little vertical illumination on walls.
Bottom line
This lm to lux calculator gives a fast and practical way to estimate illuminance for homes, offices, studios, and workspaces. Enter lumens, enter area, and you get a clear lux target to guide your lighting decisions.