Lux to Foot-candles

How Many Foot-candles in a Lux?

To convert lux to foot-candles, divide the lux value by 10.764. The formula is fc = lx ÷ 10.764. For example, 500 lux equals approximately 46.5 foot-candles. This conversion is one of the most frequently needed in lighting design, architecture, and workplace safety. Lux is the SI unit of illuminance, measuring the amount of luminous flux (light) landing on one square meter of surface, while the foot-candle measures the same concept using one square foot as the reference area. Since lux is the global standard while foot-candles remain widely used in the United States and Canada, anyone working across international lighting standards must be comfortable converting between them. Building codes, OSHA workplace requirements, photography light meters, and horticultural grow-light specifications all reference one or both of these units. Understanding the conversion helps you ensure that a space meets its lighting requirements regardless of which unit the specification uses. It also matters during commissioning, when a field lux meter has to be compared with an American schedule written in foot-candles. Quick conversion helps you verify compliance before changing fixture aiming, dimming levels, or mounting height.

How to Convert Lux to Foot-candle

1. Identify the illuminance value in lux (lx) that you want to convert.
2. Divide the lux value by 10.764 to get the equivalent in foot-candles.
3. The result is the illuminance expressed in foot-candles (fc).
4. Quick estimate: divide by 10 and subtract about 7% for a fast approximation.
5. For very rough work, simply divide by 10 — the error is under 8%.

Real-World Examples

History of Lux and Foot-candle

The lux was established as part of the International System of Units (SI) and derives from the Latin word for light. It is defined as one lumen per square meter, tying it directly to the fundamental photometric unit of luminous flux. The lux became the standard unit for illuminance in most countries during the 20th century as the metric system spread through international standards organizations. The foot-candle has a longer history in English-speaking countries, originating in the era when candles were the primary artificial light source. One foot-candle was defined as the illumination produced by a standard candle at a distance of one foot — a charmingly intuitive definition that made it easy for early lighting engineers to reason about illumination levels. As lighting technology evolved from candles to gas lamps to incandescent bulbs and now LEDs, the foot-candle survived as a measurement standard in the United States, embedded in building codes, IESNA (Illuminating Engineering Society of North America) guidelines, and OSHA workplace safety regulations. The conversion factor of 10.764 arises directly from the relationship between square meters and square feet: one square meter equals approximately 10.764 square feet. Since both lux and foot-candles measure lumens per unit area, the conversion is simply the ratio of the two area units.

Common Mistakes to Avoid

• Multiplying instead of dividing. To go from lux to foot-candles, you divide by 10.764. Multiplying converts in the wrong direction and produces a value roughly 116 times too large.
• Confusing illuminance (lux, foot-candles) with luminous intensity (candela) or luminous flux (lumens). Lux and foot-candles measure light arriving at a surface, not light emitted by a source.
• Using a rounded factor of 10 instead of 10.764. While convenient for rough estimates, this introduces a 7.6% error that can matter in lighting design where codes specify minimum illuminance levels.
• Comparing a converted value with the wrong measurement plane. Lux and foot-candle targets are usually specified at desk height, floor level, or another task surface, so converting accurately does not help if the reading was taken at the wrong location.

Frequently Asked Questions