Light Intensity Calculator
Calculate light intensity variation with distance using the inverse square law: I = P / (4 * pi * r²).
Intensity
1.9894 W/m²
Intensity vs Light Source Power
Formula
## Light Intensity (Inverse Square Law) Light intensity from a point source decreases with the square of the distance. ### Formula **I = P / (4 * pi * r²)** where P is the total power output and r is the distance from the source. Doubling the distance reduces intensity by a factor of four.
Esempio Risolto
A 100 W light bulb at 2 meters distance.
- 01I = P / (4*pi*r²)
- 02I = 100 / (4*pi*4)
- 03I = 100 / 50.27
- 04I = 1.989 W/m²
Domande Frequenti
Why does the inverse square law apply?
A point source radiates uniformly in all directions. The same power spreads over an ever-increasing spherical area (4*pi*r²), reducing intensity.
What is the intensity of sunlight at Earth?
About 1361 W/m² above the atmosphere (the solar constant). At the surface, roughly 1000 W/m² on a clear day.
Does this apply to laser beams?
Not directly. Lasers produce a collimated beam that spreads slowly (governed by diffraction), so intensity drops much more slowly than 1/r².
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