Convert foot-candle [ft*c, fc] to candela steradian/sq. meter Online | Free lllumination Converter

A Unit of Illuminance

The foot-candle (ft·c or fc) is a unit of illuminance used primarily in the United States and some other countries that follow imperial measurements. It measures the amount of luminous flux (light) falling on a surface of one square foot. One foot-candle is defined as one lumen per square foot.

Foot-candles are commonly used in lighting design, architecture, photography, and workplace safety to ensure spaces have appropriate lighting levels. For example, an office workspace typically requires around 30 to 50 foot-candles to provide sufficient brightness for tasks without causing eye strain. Retail stores and hospitals may require higher levels, while hallways or staircases might have lower standards.

Foot-candles are related to the metric unit lux, where 1 foot-candle equals approximately 10.76 lux (lumens per square meter). Understanding foot-candle measurements allows designers and engineers to plan lighting layouts effectively, balancing energy use with visual comfort.

Despite the growing global adoption of the lux, foot-candles remain prevalent in industries and regions that use imperial units, making it important for professionals to be familiar with both.

Understanding Radiance

Candela steradian per square meter (cd·sr/m²) is a unit of radiance, which measures the amount of light power emitted, reflected, or transmitted from a surface in a specific direction per unit area. It combines the candela (cd), which quantifies luminous intensity, with the steradian (sr), the unit of solid angle, and divides by the surface area in square meters.

Radiance describes how bright a surface appears when viewed from a particular direction and is critical in fields such as optics, imaging, computer graphics, and remote sensing. Unlike illuminance (which measures light falling on a surface), radiance tells us about the directional brightness coming off or through a surface.

This unit helps in characterizing light sources and reflective surfaces, allowing scientists and engineers to model how light behaves in complex environments. It is essential for designing lighting systems, calibrating cameras, and simulating realistic visual scenes.

Understanding candela steradian per square meter allows precise control over brightness and directional light properties, supporting advancements in display technology, vision science, and photometric measurements.