Roll your mouse over the picture to enlarge the leave.

On the window sill

Unfortunately, your answer is wrong.

Leaves only become lighter, when they get very little light. The light which is reflected towards them by the surrounding is sufficient normally.

The leaves have been damaged because of the irregular form of the glass.
Sunlight passes normal window panes nearly unchanged, so that the leaves are uniformly illuminated. But this window consists of irregularly formed elements. Thereby the light is deflected in different directions und partly focussed on small areas.

But what is it actually that focusses the light?
If you are unsure, firstly look at this hint !

a) If the light passes through roundly outward curved areas, the light beams are deflected and come together.

b) The light can hardly pass the intersections of the wavy pattern of the pane. Instead of that it passes through the other areas, so the intensity of the light is stronger there.

c) The light especially gets into the roundly inward curved areas of the window. There it is collected similar to a funnel.