Geometry-Dependent Illuminance Decay and the Limits of the Inverse-Square Law
A demonstration, via a smartphone-sensor open-inquiry laboratory, that the distance dependence of illuminance is set by the geometry of the light source: inverse-square for point sources, inverse-linear for line sources, nearly constant for flat sources within their size, and non-monotonic (peaking at an intermediate distance) for ring sources. It uses measured light curves and model fits to delineate each law's range of validity and the sensor-directivity effects that bound it.
2501.00622
An open-inquiry physics laboratory that uses the light sensors built into smartphones to measure how illuminance decays with distance for light sources of different geometries, showing where the fami…