The Inverse Square Falloff & Diffuse Window Physics
While point sources like bare light bulbs follow the pure inverse-square law, an architectural window behaves as an area diffuse emitter up close. However, as you step back beyond 1.5–2 meters, the effective solid angle of visible sky collapses rapidly. Moving a plant just 2 meters back from a window slashes available photosynthetic photons to less than 20% of what is available right on the sill.
Defining Indirect Sunshine
Bright indirect light means the plant can 'see' the open sky clearly through the glass without direct thermal sunbeams burning its leaves. Think of sitting under the canopy of a large tree on a sunny noon.
Assessing Foliar Clues
Plants starved of light produce elongated stems with large spaces between leaves (internodal stretching) and smaller, paler leaves. Plants receiving healthy light maintain compact silhouettes and vigorous venation.