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Photon energy from wavelength
Convert vacuum wavelength in nanometres into the energy of one photon in joules and electronvolts using Planck’s constant and light speed.
Calculators / Science / Inverse square intensity
Inverse square intensity calculator
Estimate intensity at a new distance from an isotropic point source by multiplying the original intensity by the squared distance ratio.
On this page
New intensity25W/m²
Intensity ratio0.25
Calculator controls
How to calculate
Estimate intensity at a new distance from an isotropic point source by multiplying the original intensity by the squared distance ratio.
New intensity = I*(a/b)^2 W/m²; Intensity ratio = (a/b)^2
Worked example
Initial intensity (W/m²): 100; Original distance (m): 2; New distance (m): 4.
New intensity: 25 W/m²; Intensity ratio: 0.25 .
Assumptions and limits
Estimate intensity at a new distance from an isotropic point source by multiplying the original intensity by the squared distance ratio. Photon wavelength is in vacuum. The inverse-square model assumes an unobstructed point source without absorption; intensity has units of power per area.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate intensity at a new distance from an isotropic point source by multiplying the original intensity by the squared distance ratio.
When this tool is useful
New intensity = I*(a/b)^2 W/m²; Intensity ratio = (a/b)^2
Understanding your inputs
| Input | What to enter |
|---|---|
| Initial intensity (W/m²) | Enter a number of at least 0 and no more than 1000000000000. |
| Original distance (m) | Enter a number of at least 1e-12 and no more than 1000000000000. |
| New distance (m) | Enter a number of at least 1e-12 and no more than 1000000000000. |
Frequently asked questions
What assumptions does this calculation use?
Estimate intensity at a new distance from an isotropic point source by multiplying the original intensity by the squared distance ratio. Photon wavelength is in vacuum. The inverse-square model assumes an unobstructed point source without absorption; intensity has units of power per area.
How is the result calculated?
New intensity = I*(a/b)^2 W/m²; Intensity ratio = (a/b)^2