Consider a 1 cd isotropic illuminance light source. answer the following:
a. what is luminance of light 10 ft from the source?
b. how much total light falls on a 1 str patch that is 10 ft from this light?

The luminance of light and the amount of light are and .

Explanation:

Given that,

Illuminance of light = 1 cd

Solid angle = 1 str

(a). We need to calculate the luminance

The luminance is the luminance intensity per unit area

(b). We need to calculate the amount of the light

Using formula of luminous flux

The luminous flux is equal to the product of the luminance intensity  and solid angle.

Where,=solid angle

I = luminance intensity

Put the value into the formula

The area of a patch on a sphere which is substand by a solid angle

We need to calculate the amount of light received by the surface

Where, = luminous flux

A= area

Put the value into the formula

Hence, The luminance of light and the amount of light are and .

your answer is c! hope this : )