Please help me with this problem. # An isotropic point source of 100 candela is fastened to the ceiling of a room. What is the total luminous flux falling on all the walls and floor? I solved it in the following way: Here Luminous intensity(I) = 100 cd, Total solid angle(w) = 2 (pi) steradian Total luminous flux falling on all the walls and floor = I x w = 100 x 2(pi) = 100 x 2 x 3.14 = 628 lumens Is it right?
I thought the walls and the floor subtended a hemispherical solid angle at the ceiling. Could you please explain how the solid angle is (pi)?
There are (pi) radians in a half circle. But I think there are 4(pi) steradians in a sphere. So there are 2(pi) steradians in a hemisphere. Solid angle(w) = Area of hemisphere/R^2 = [2(pi)R^2]/R^2 = 2(pi) steradians I think radian is a 2 dimensional unit whereas steradian is a 3 dimensional unit of angle. I may be wrong.
No. You are right. A sphere subtends [itex]4\pi[/itex] steridians, so the hemisphere is [itex]2\pi[/itex]. Sorry about confusing you. AM