Plants exhibit phototropism, a growth response to light. Auxin, a light-sensitive hormone found in leaf and stem tips, drives this phenomenon. Shoots display positive phototropism, bending towards light, while roots exhibit negative phototropism, bending away from it. For instance, sunflower heads, being positively phototropic, follow the sun's movement from east to west.
Write the equation for the relationship as on a logarithmic scale.