Increasing intensity of light induces increasing tropic curvature.
Tropic curvature increases with the directive angle, the effect being approximately proportional to sin θ, where θ is the angle made by the rays with the responding surface.
Tropic curvature also increases with the duration of exposure.
The intensity of induced tropic effect is determined by the quantity of incident light.
[14] The directive angle θ is the angle of inclination of the rays of light to the responding surface. The angle θ is complementary to the angle of incidence i in optics. Sin θ = Cos i.
[15] An explanation of this preliminary effect will be found in the next chapter.