What Is an Illumination Converter?
An illumination converter is an essential tool designed to translate the measurement of illuminance across different metric, imperial, and radiometric systems. By rapidly determining equivalent values, this calculator helps lighting designers, photographers, scientists, and engineers ensure optimal and standard-compliant lighting environments.
Illuminance refers to the total luminous flux incident on a surface, per unit area. In simpler terms, it's a measure of how much the incident light illuminates the surface. The standard International System of Units (SI) measure for illuminance is the lux (lx), representing one lumen per square meter. However, depending on geographic location and the industry (like the film industry, agriculture, or architectural lighting), other units such as the foot-candle (fc) or watt per square meter are regularly used.
How to Use This Converter
Using our online converter to calculate illumination units is straightforward. Just follow these simple steps:
- (Optional) Filter by Group: If you are looking for a specific type of unit—such as Metric or Imperial units—use the dropdown above the input box to narrow down the list.
- Enter Your Value: Type the numerical value of the illumination you wish to convert in the "Enter Value" box.
- Select Your Units: Choose your starting unit in the From dropdown and your target unit in the To dropdown.
- Convert: Click the "Convert" button. Your direct translation will appear immediately alongside a convenient reference table detailing the conversion across all available units.
Understanding the Unit Groups
Our illumination converter categorizes units into distinct groups to help streamline your workflow. Understanding these groupings can give you better insight into the origin and standard application of each measurement scale.
Metric / SI Units
The International System of Units (SI) focuses heavily on the lux (lx) as its core measurement of illumination, equal to one lumen per square meter. Metric units are standard for modern engineering, global scientific research, and workplace lighting compliance. This group includes units like the meter-candle (equivalent to lux), centimeter-candle, phot (equivalent to 10,000 lux), nox, and candela steradian per square meter.
Imperial / US Customary Units
Primarily used in the United States by architects, the construction industry, and within certain photography fields, imperial illuminance units calculate luminous flux distributed over a square foot or square inch. The most recognizable unit in this category is the foot-candle (fc), mathematically defined as one lumen per square foot. Other units found here are the lumen per square foot and lumen per square inch.
Other & Radiometric Units
This category encompasses historical units such as the "flame" alongside strictly radiometric units like watts per square meter (W/m² at 555 nm) and watts per square centimeter. Radiometric terms are exceptionally useful when measuring radiant power at specific human visual sensitivity wavelengths, primarily the 555-nanometer green-yellow spectrum where human eye sensitivity peaks.
Common Illumination Conversions
While an extensive list of units exists, a few specific conversions are requested far more frequently than the rest. Here is a breakdown of the most common illuminance conversions utilized in real-world scenarios:
- Lux to Foot-Candles: Since 1 foot-candle equates to approximately 10.76 lux, converting lux to foot-candles requires dividing the lux value by 10.76 (or multiplying by 0.0929). For example, a 500 lux office is roughly 46.5 foot-candles.
- Foot-Candles to Lux: Multiply the foot-candle value by 10.7639. A space requiring 30 foot-candles needs approximately 323 lux.
- Phot to Lux: A phot (ph) is an older CGS unit. One phot is equal to 10,000 lux. Therefore, 2 phots amount to 20,000 lux.
- Lumen/Square Meter to Lux: This is a 1-to-1 direct conversion. 100 lm/m² is exactly 100 lux.
- Watt/m² (at 555 nm) to Lux: At the peak efficiency of human vision, 1 Watt/m² translates to exactly 683 lux. This conversion is heavily utilized in solar physics and specialized lighting manufacturing.
Tips for Accurate Conversion
To avoid costly mistakes in lighting setups, whether for an indoor hydroponics farm or a corporate building, keep these pointers in mind:
- Know the difference between Illuminance and Luminous Flux: Illuminance (lux, foot-candles) dictates how bright a surface appears, whereas luminous flux (lumens) measures the total amount of light leaving the source. Do not interchange them.
- Check the Peak Wavelength: When converting between radiometric units (watts) and photometric units (lux), ensure the calculation considers the 555 nm peak wavelength standard unless you are specifically measuring for plants (PAR) which uses a different calculation entirely.
- Surface Area Matters: A 1000 lumen bulb will provide 1000 lux if concentrated on a 1 square meter surface. If that same beam spreads over 10 square meters, the illuminance drops to 100 lux. Keep distance and spread in mind when interpreting calculations.
Frequently Asked Questions
How do you convert lux to foot-candles?
To convert lux to foot-candles, multiply the lux value by 0.092903. Conversely, one foot-candle is equal to exactly 10.76391 lux.
What is the difference between lux and lumens?
Lumens measure the total amount of light emitted by a source (luminous flux), while lux measures the amount of light that falls on a specific area (illuminance). One lux equals one lumen per square meter.
What is a foot-candle?
A foot-candle is a non-SI unit of illuminance used primarily in the United States. It represents the illumination produced by one candela of light falling on a one-square-foot surface from a distance of one foot.
How does watt per square meter relate to lux?
The conversion between watts per square meter (irradiance) and lux (illuminance) depends on the wavelength of light. At the peak human visual sensitivity of 555 nanometers (green light), 1 watt per square meter equals exactly 683 lux.
What is a phot in lighting?
A phot is a unit of illuminance in the older CGS (centimeter-gram-second) system. One phot is equivalent to 10,000 lux or one lumen per square centimeter.