Foot Candles to Lux Converter

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Illuminance: Light landing on a surface. Both foot-candles and lux measure illuminance.

Foot-candle (fc): Illuminance based on lumens spread over one square foot; it is common in US lighting work.

Lux (lx): Illuminance based on lumens spread over one square meter; 1 lx equals 1 lumen per square meter [2].

Conversion factor: The number multiplied by the starting reading to get the target unit before rounding.

Decimal places: The number of digits shown after the decimal point in the displayed answer.

Scientific notation: A compact way to show very small or very large numbers, such as 1.23e+6 for 1,230,000.

Mistake: Picking the wrong Convert direction and getting the inverse answer.
Fix: Read Plain English check after calculating and switch Convert if the start unit is backwards.

Mistake: Typing a lux reading into Light amount (foot-candles) .
Fix: Use Light amount (lux) when your meter shows lx, or change Convert to Lux to foot-candles .

Mistake: Entering words, unit symbols, or a negative value in Light amount (lux) or Light amount (foot-candles) .
Fix: Enter only a number, such as 500 or 50; zero is allowed, but negative illuminance is not.

Mistake: Setting Decimal places too low and thinking the exact calculation changed.
Fix: Increase Decimal places ; rounding changes only the displayed Converted light amount .

Mistake: Pasting mixed units into Extra readings (one per line, same start unit) .
Fix: Use only readings in the same start unit chosen by Convert , one number per line.

Mistake: Comparing Converted light amount to a chart that uses 10.76 instead of the full factor.
Fix: Check Conversion factor used and expect tiny differences from tools that round the factor early.

• The conversion changes units only. It does not judge whether a room, workspace, plant area, camera setup, or code requirement has enough light.
• The calculator assumes the reading is illuminance on a surface. It does not convert brightness of a light source, lumens, candela, watts, or exposure settings.
• Displayed answers are rounded according to Decimal places. The internal multiplication uses the full stored conversion factor.
• Number format affects display only. In Auto format, scientific notation is used only when the absolute converted value is nonzero and below 0.0001, or at least 1,000,000.
• Extra readings (one per line, same start unit) must use the same start unit as the main conversion direction. Blank lines are skipped.
• Very large entries must still be finite numbers. If the result would exceed normal computer number limits, the calculator blocks the input instead of showing Infinity.

How the conversion is done

The converter reads only the active start-unit field selected by Convert. For Foot-candles to lux, it reads Light amount (foot-candles). For Lux to foot-candles, it reads Light amount (lux). The other unit field is ignored so a hidden value cannot change the result.

lux = foot_candles * 10.763910416709722

foot_candles = lux * 0.09290304

These factors come from area units. One square foot is 0.09290304 square meter, and illuminance compares lumens over area, so 1 foot-candle equals 1 divided by 0.09290304 lux, or 10.763910416709722 lux [1].

Rounding and number format

The raw converted value is calculated first. Then the displayed value is rounded to the selected Decimal places.

display_value = round(raw_value, decimal_places)

Number format controls only how the answer is printed. Auto uses normal decimals for everyday values, but switches to scientific notation when the absolute converted value is nonzero and below 0.0001, or at least 1,000,000.

Mini example

If Convert is Foot-candles to lux and Light amount (foot-candles) is 50, the raw result is 50 * 10.763910416709722 = 538.1955208354861 lux. With Decimal places set to 2, Converted light amount is 538.20 lx.

Extra readings

Each nonblank line in Extra readings (one per line, same start unit) is parsed as a separate reading. The same conversion direction, conversion factor, rounding setting, and number format are applied to every valid line. If any nonblank line is not a finite nonnegative number, the calculator asks you to fix that line before showing the table.