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Architect’s Handbook of Formulas, Tables, and Mathematical Calculations by David Kent Ballast

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Chapter 2F. Illumination

Measuring Light and Illumination Terms

(See Figure 2F-1.)

Relationship of Light Source, Illumination, Transmittance, and Reflectance

Figure 2F-1. Relationship of Light Source, Illumination, Transmittance, and Reflectance

Luminous Intensity, I, is the solid angular flux density in a given direction measured in candlepower in American Standard (AS) units and candela in SI units. The candela and candlepower have the same magnitude.

Lumen, lm, is the unit of luminous flux equal to the flux in a unit solid angle of one steradian from a uniform point source of one candela. On a unit sphere, an area of one square foot (or square meter) will subtend an angle of one steradian. Since the area of a unit sphere ...

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