All plants grew towards the glass window. The part exposed to light grows slower than the one that is not exposed. Blue, violet and ultraviolet light together have the same effect as very strong white light. The effect remains even after the UV part is taken away. Red, yellow , and green light has no effect on most plants.
Red light causes a phototropic reaction in some fern prothalliums, though.
The amount of light and the phototropic reaction are linked. The Bunsen-Roscoe law states that the product of time and intensity, and thus the energy amount of the used light, is the measure of the stimulus strength. It is thus of no importance whether a light stimulus of low intensity is applied for a longer period of time or whether a stimulus of high intensity is applied for a short time. The amount of white light is given in lux seconds, the ordinate gives the positive or negative bending. Positive and negative phototropism within the same tissue are characteristic not only for Avena coleoptiles.