Convert watts to lux, or lux to watts, for a given area using typical LED, CFL, halogen or incandescent efficacy, or enter your own lumens per watt.
- All Unit Converters
- Watts to Voltage Calculator
- Waves, Optics and Quantum Unit Converters
- Watts to Lumens Calculator
- Lumens to Lux Distance Calculator
- Light Intensity Calculator
- Average Foot Candle Calculator
Watts To Lux Formula
The following formula estimates average illuminance (lux) when all emitted lumens reach the area with no maintenance loss. The calculator includes utilization U and maintenance M: L = W ร E ร U ร M / A, starting at U = 0.8 and M = 0.9.
Variables:
- L is the illuminance in lux (lx)
- W is the power in watts (W)
- A is the area in square meters (mยฒ)
- 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 โwatts to luxโ conversionโresults depend on luminous efficacy, the area being lit, and (in real lighting layouts) how much of the emitted light actually reaches that area.
Lux to W/mยฒ of Light
The irradiance modes convert between illuminance in lux and incident radiant power per area in W/mยฒ. Choose a radiation spectrum assumption, then enter lux to estimate irradiance or enter irradiance to estimate lux. These modes describe light arriving at the same surface and plane, rather than the electrical power drawn by a lamp.
For a known spectrum, illuminance Ev (lux) = irradiance Ee (W/mยฒ) ร K (lm/W), and Ee = Ev รท K. Here K is the luminous efficacy of radiation: visible-light output weighted for human photopic vision per radiant watt. It differs from a fixtureโs lumens per electrical watt.
The 683 lm/W assumption applies to monochromatic light at 540 THz, approximately 555 nm. Sunlight and white LEDs have varying spectra, so neither has one universal lux-to-W/mยฒ factor. For broadband light, enter a measured or spectrum-derived K for the full optical band included in the irradiance reading. Using a visible-band factor with a reading that includes infrared or ultraviolet can give a misleading result.
| 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 mยฒ, luminous efficacy ฮท = 100 lm/W, utilization U = 1 and maintenance M = 1. Formula: E (lx) = P (W) ร ฮท (lm/W) / A (mยฒ). 1 fc = 1 lm/ftยฒ โ 10.7639 lx. For other areas/efficacies, lux scales linearly. | ||
What is Watts To Lux?
โWatts to luxโ describes estimating illuminance (lux) from electrical power (watts) when you also know the light sourceโs 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 (mยฒ).
- Next, determine the luminous efficacy in lumens per watt (lm/W).
- For adjusted results, use L = (W ร E ร U ร M) / A. Set both light factors to 1 for the unadjusted formula and table.
- 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 (mยฒ) = 10
luminous efficacy in lumens per watt (lm/W) = 20. With U = M = 1, the result is 100 lux; with the calculatorโs default U = 0.8 and M = 0.9, it is 72 lux.
