Lighting Calculator
Estimate how much light a room needs and how many bulbs you should plan for.
The formula uses room area and target illuminance, then compares that to the output of one bulb.
Lighting Result
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Bulbs needed: --
Room area: --
Run the calculation to see the lumen breakdown.
Quick Answer
Lighting needs are usually estimated as area x illuminance. If a room needs 1,200 lumens and one bulb provides 800 lumens, you need two bulbs.
How to Calculate Lighting
- Measure the room area.
- Choose the target lux or foot-candles for the space.
- Multiply area by illuminance to get required lumens.
- Divide by bulb lumens to estimate the bulb count.
Formula
Required lumens = area x target illuminance
Bulbs needed = required lumens / lumens per bulb
Worked Examples
Example 1: A 5 m by 4 m room at 300 lux needs about 6,000 lumens.
Example 2: A 12 ft by 10 ft room at 30 foot-candles needs about 3,600 lumens.
Example 3: If each bulb gives 800 lumens, 6,000 lumens means you need 8 bulbs.
How to Interpret Your Results
| Output | Meaning | Action |
|---|---|---|
| Higher lumen requirement | The room is larger or needs brighter light. | Use more bulbs or brighter fixtures. |
| Lower lumen requirement | The room is smaller or only needs task lighting. | Choose a softer lighting setup. |
| Bulb count rounds up | You cannot buy part of a bulb. | Always round up to the next whole bulb. |
Frequently Asked Questions
Lux measures how much light lands on a surface, with one lux equal to one lumen per square meter.
A foot-candle is the imperial version of illuminance and measures lumens per square foot.
Either works. More bulbs spread the light more evenly, while brighter bulbs raise the total output faster.
Related Calculators
References
- OmniCalculator reference page
- Lighting calculations are based on area and target illuminance.
- Last reviewed: March 2026.