Look how this young cottonwood leaf glows with light, and how the older leaves (by just a day or two), now full of chlorophyll, keep much of it.

Here’s a similar effect in a lilac planted beneath a larger cottonwood, and catching some shade. Here the difference between the unlit cells of the leaf and the lit ones is equally dramatic, as the chloroplasts reflect light photons twenty times before they are either eaten (1 in 2000) or radiated further.

These leaves really do glow!