Thank you for your help! Question- Explain why a one fc (foot-candle) equals one

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Question- Explain why a one fc (foot-candle) equals one Lumen / ft2 Let's reason this out as follows Place an isotropic source at the center of sphere, with a luminous intensity of I = 1 candela Select a solid angle stemming from the Center. Solid angle = 1 steradian Question- What is the luminous flux in the solid angle Q? Luminous flux = cp = also write the units Let the sphere have a radius = 1 ft. What is the surface area? A = ft2 So we have placed a candle at a distance of 1 foot, from the surface From 3 and 4, find the Illuminance E = cp / A = In what units?

Explanation / Answer

3) luminous flux= 1 Lumen

4) surface area= 4*pi*r^2=4pi*1=4pi ft^2

6) Luminanc =(1 Lumen)/(4pi ft^2)=(1/4pi)Lumen/ft^2

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