Phosphorescence in an Atlantic Giant Cockle shell(Dinocardium robustum). The Atlantic Giant Cockle, also known as the Great Heart Cockle, is the most common cockle, out of the seven found in the United States. This large and sturdy shell can grow up to 5 inches in length and is creamy white to tan in color, although some have dark, reddish-brown spots. To image the phosphorescent property the shell was illuminated with a very bright UV flash before the camera shutter was opened. The camera was able to capture the light from the sample as the excited electrons fell back to their ground state and emitted light. Image #2 of 2 in a sequence.