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Illumination Converter

Convert illumination values quickly and accurately. Instant conversions with detailed step-by-step solutions.

Last Updated: May 26, 2026
5 min read

About this converter

Convert between 12 different units of illumination. Enter a value and select units to see the conversion result instantly with step-by-step solution.

Need to convert a light measurement from one unit to another? The Illumination Converter does that for you. Enter a number, pick the unit you measured, and the calculator instantly converts it into other common illumination units such as lux and foot-candles. It's useful for lighting designers, electricians, facility teams, photographers, students, and DIY users everywhere. The tool gives you the same light level in matching units, so you can compare readings from different meters, apps, or specs without guesswork.

How to Use This Calculator

  • Enter your illumination value (the number you measured).
  • Select the unit you currently have (for example, lux or foot-candle).
  • Choose the unit you want to convert to.
  • Review the converted result shown by the calculator.
  • If needed, change the value or units to compare multiple readings.

What This Calculator Measures

This calculator converts illuminance, which means how much light falls on a surface. Illuminance is different from "how bright a bulb is." A bulb's output is about the light it produces, while illuminance is about the light that actually reaches a desk, floor, wall, or work area.

Key terms (simple meanings):

  • Illuminance: Light arriving on a surface.
  • Lux (lx): Illuminance measured as lumens per square meter.
  • Foot-candle (fc): Illuminance measured as lumens per square foot.
  • Phot (ph): Illuminance measured as lumens per square centimeter (an older unit).

Formula or Logic (Easy Explanation)

The converter uses fixed relationships between units. For example:

  • Lux and foot-candles are linked by a constant area conversion between square meters and square feet.
  • Lux and phot are linked by a constant area conversion between square meters and square centimeters.

In simple terms, the tool first translates your value into a standard reference (usually lux), then converts that same light level into your chosen unit.

Example Calculations

Example 1: Lux to Foot-candles

  • Input: 500 lux
  • Output: 46.45 foot-candles (approx.)

Example 2: Foot-candles to Lux

  • Input: 100 foot-candles
  • Output: 1076.39 lux (approx.)

Example 3: Phot to Lux

  • Input: 2 phot
  • Output: 20,000 lux

Understanding Your Results

Your result is the same illumination level, just expressed in a different unit. If the number looks "bigger" or "smaller," that does not mean the light changed. It only reflects the size of the unit. For example, lux is based on square meters, while foot-candles are based on square feet, so the numeric values often differ. If you are comparing two locations, make sure both readings were taken at the same height, angle, and distance from the light source.

Common Mistakes to Avoid

  • Mixing up lux (illuminance) with lumens (light output).
  • Forgetting that illuminance depends on distance from the light source.
  • Comparing readings taken with different meter settings (auto range, averaging, etc.).
  • Measuring at different angles (tilting the sensor changes results).
  • Converting correctly but using the result for the wrong surface size.
  • Confusing foot-candle with candlepower (they are not the same).
  • Rounding too early when you still need to do more conversions.

Frequently Asked Questions

Lux is light on a surface (illumination). Lumens are total light produced by a source. You can't convert lumens to lux without knowing the area and setup.
Enter your lux value, select lux as the input unit, and choose foot-candles as the output unit. The calculator applies the fixed conversion factor automatically.
Illuminance changes with distance, shadows, beam angle, and reflections. A desk near a lamp can read much higher than a corner across the room.
Yes. Both describe illuminance. The difference is the unit system: foot-candles are common in the US, while lux is common internationally.
Not directly. Lux measures light per area. To estimate lumens, you need the surface area (and real-world conditions can still affect accuracy).
Phot is an older illuminance unit based on square centimeters. It represents light per cm², so it converts to lux using a fixed area relationship.
Not exactly. Illuminance measures light arriving on a surface. Perceived brightness also depends on contrast, color temperature, glare, and adaptation.
Phones are not calibrated like dedicated light meters. Sensor differences, camera settings, and app algorithms can cause noticeable variation.
Most lighting specs use lux (international) or foot-candles (US). Use the unit that matches your standard, building documents, or device.
The conversions themselves are exact relationships between units. The main source of error is usually the original measurement method or device.

Illuminance conversion is simple when you use the right units. This Illumination Converter helps you switch between lux, foot-candles, phot, and other related formats so your readings stay consistent and comparable. Try the calculator above to see your results.