Question

The luminous intensity of a small plane source of light along the forward normal is $160cd$. Assuming the source to be perfectly diffused, the luminous flux emitted into a cone of solid angle $0.04str$ around a line making ${60}^0$ with forward normal is:

• A. $3.2lm$
• B. $0.8lm$
• C. $16lm$
• D. $1.6lm$

Answer 1

Answer: (A)

$3.2lm$

Intensity $I=I_o\cos \theta =160\cos {60}^o=80cd$

Flux $\Phi =I\Omega =80\times 0.04=3.2lm$