A natural light source eliminates the falloff given the suns distance, dispersion of the reflected light has the same falloff as mentioned above. Enclosing a tent around a LED tube or bulb will greatly reduce the falloff, while one sq inch will disperse the light in 180 degrees leading to falloff, the sq inch next to it will do the same augmenting the light lost by the first inch on the targeted leaf. If you do this with a window as your light source and avoid shading the reflector with the tree you will see next no falloff, the shaded side becomes almost as bright as the sunny side. The angle and position must be considered, a reflector angle at 45 degrees with vertical source will light the edge of the leaf, not very useful, a 45 degree light source and vertical reflector positioned above the targeted leaf will light the top of the leaf. A light meter would be very valuable for placement.