Suppose that you look into the photometer’s eyepiece and the fluorescent disks appear to be equal in intensity. if the distance between the photometer to lamp 1 is 500 mm, the distance between the photometer to lamp 2 is 300 mm, and the intensity of lamp 2 is known to be 17 candelas, what’s the intensity of lamp 1?

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).

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