How many lumens are equivalent to one candlepower?

One candlepower, now referred to as candela in the International System of Units (SI), is a measure of luminous intensity in a specific direction. To convert this intensity into lumens, which measure the total quantity of visible light emitted in all directions, a relationship is established based on a standard solid angle.

One candela is equivalent to approximately 12.57 lumens when considering it spans one steradian, which is a unit of measure for solid angles. This stems from the formulas used in photometry where 1 lumen is defined as the amount of light emitted in a solid angle of one steradian by a point source with a luminous intensity of one candela.

This is the basis for the correct answer being 12.57 lumens per candlepower, as it accurately conveys the mathematical and physical relationship between these two units of measurement widely used in lighting and visual sciences. Understanding this conversion is crucial for applications that involve lighting design, energy efficiency calculations, and other fields that require precise light measurements.