Foot Candle (fc) – The Imperial Unit of Illuminance

Thefoot-candleis an imperial unit used to measure illuminance. It is defined as the illuminance on a surface that is one foot away from a uniform point light source. Essentially, one foot-candle is equivalent to one lumen per square foot.

Definition & Background

Although not part of the SI system, the foot-candle remains popular in the United States and other regions that use the imperial system. It offers a practical way to assess lighting in environments like offices, theaters, and sports facilities.

Conversion Factors

• 1 foot-candle ≈ 10.764 lux
• 1 lux ≈ 0.092903 foot-candles

Applications

Foot-candles are widely used in the design and assessment of lighting in:

• Interior and architectural lighting, to ensure spaces have adequate brightness.
• Sports fields and outdoor arenas, where consistent illumination is critical.
• Retail and commercial environments, ensuring proper display lighting for merchandise.

Interesting Facts

• Lighting designers often use foot-candles to compare the effectiveness of various lighting solutions in large spaces.
• The use of foot-candles in theater lighting is crucial for setting the mood and ensuring that scenes are properly illuminated.

Conclusion

The foot-candle is a practical unit for measuring illuminance in environments where the imperial system is in use. Its straightforward conversion to lux makes it a valuable tool in both design and application, ensuring spaces are lit efficiently and effectively.