How does brightness change with distance? Explore all the laws β then find the real one.
3.0 m
800 cd
Inverse Square LawThe Real Law
B = Iβ / rΒ²
B = Iβ / rΒ²β
Linear LawAlternative
B = Iβ / r
B = Iβ / rβ
Brightness vs. Distance β All Laws at a Glance
π The Real-World Challenge
You walk away from a candle, doubling your distance from 1 m to 2 m.
By which factor does the brightness drop? Choose the answer that matches the real law.
Why ΒΌ?
The Inverse Square Law comes from geometry. Light radiates in all directions from the candle,
spreading over a sphere of surface area 4ΟrΒ². When you double your distance, the same energy
spreads over 4Γ the area β so each part of the sphere gets only 1/4 the intensity.
Mathematically: B β 1/rΒ² β at r = 2: B β 1/4. This is why distant stars appear so faint,
why architects carefully place lights, and why astronomers use it to measure stellar distances!