Solid Angles, Surfaces of Spheres and the Steradian

Imaginary Sphere Surrounding

a point source of light

Sphere Area = 4pr2

r

ie., distance

Area

1 m2 subtends 1 sr at a

distance of 1 m…since

Surface area of a sphere

is subtended by 4p sr

w = A = 4pr2 =

r2

4p

r2

4p = 12.56

Previous slide

Next slide

Back to first slide

View graphic version