These two “petal-pushing” images start with a composition of alstroemeria petals, photographed for high-key HDR on a light box. 

The image with a black background (shown above) is an LAB L-channel inversion of the original image on white, shown below.

Generally, with light box compositions, the most important issue is the arrangement, a/k/a the composition. By the way, this is a statement that could be made (and has been made) about photography in general.

Arrangement needs structure. One of the most common structures for light box compositions is the Mandala. Another is the bouquet (click here for an example).

Can you identify the visual structure underlying the Petals on Parade images?