47.22 Candelas
s₁ = 500 mm; distance between the photometer to lamp 1.
s₂ = 300 mm; the distance between the photometer to lamp 2.
I₂ = 17 cd; the intensity of lamp 2.
Using the formula;
I₁ = I₁ · (s₁² ÷ s₂²).
I₁ = 17 cd · (250000 mm² ÷ 90000 mm²).
I₁ = 47.22 cd;
Thus; the intensity of lamp 1 is 47.22 cd
Candela is the base unit of luminous intensity in the International System of Units (SI).