Enter the power, illuminated area, and luminous efficacy into the calculator to estimate the illuminance. This calculator can also evaluate any one of the variables when the other three are known.
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Watts To Lux Formula
The following formula is used to estimate illuminance (lux) from electrical power when luminous efficacy and illuminated area are known.
L = \frac{W \cdot E}{A}Variables:
- L is the illuminance in Lux (lx)
- W is the power in Watts (W)
- A is the area in square meters (m²)
- E is the luminous efficacy in lumens per watt (lm/W)
To calculate illuminance in lux, multiply the power in watts by the luminous efficacy in lumens per watt to get lumens, then divide by the illuminated area in square meters. This relationship is not a universal “watts to lux” conversion—results depend on luminous efficacy, the area being lit, and (in real lighting layouts) how much of the emitted light actually reaches that area.
| Power (W) | Illuminance (lx) | Foot-candles (fc) |
|---|---|---|
| 1 | 100 | 9.290 |
| 3 | 300 | 27.871 |
| 5 | 500 | 46.452 |
| 7 | 700 | 65.032 |
| 10 | 1,000 | 92.903 |
| 12 | 1,200 | 111.484 |
| 15 | 1,500 | 139.355 |
| 18 | 1,800 | 167.225 |
| 20 | 2,000 | 185.806 |
| 25 | 2,500 | 232.258 |
| 30 | 3,000 | 278.709 |
| 40 | 4,000 | 371.612 |
| 50 | 5,000 | 464.515 |
| 60 | 6,000 | 557.418 |
| 75 | 7,500 | 696.773 |
| 100 | 10,000 | 929.030 |
| 150 | 15,000 | 1,393.546 |
| 200 | 20,000 | 1,858.061 |
| 300 | 30,000 | 2,787.091 |
| 500 | 50,000 | 4,645.152 |
| Assumptions: Area A = 1.00 m², luminous efficacy η = 100 lm/W. Formula: E (lx) = P (W) × η (lm/W) / A (m²). 1 fc (ft‑lx) = 10.7639 lx. For other areas/efficacies, lux scales linearly. | ||
What is Watts To Lux?
“Watts to lux” describes estimating illuminance (lux) from electrical power (watts) when you also know the light source’s luminous efficacy (lumens per watt) and the illuminated area. Watts measures power (energy per unit time), while lux measures illuminance (lumens per square meter). There is no direct, universal conversion from watts to lux without these additional inputs and assumptions about how the light is distributed over the area.
How to Calculate Watts To Lux?
The following steps outline how to calculate the Watts To Lux using the given formula:
- First, determine the power in Watts (W).
- Next, determine the area in square meters (m²).
- Next, determine the luminous efficacy in lumens per watt (lm/W).
- Next, gather the formula from above = L = (W × E) / A.
- Finally, calculate the illuminance in Lux (lx).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following variables as an example problem to test your knowledge:
power in Watts (W) = 50
area in square meters (m²) = 10
luminous efficacy in lumens per watt (lm/W) = 20
