In most reactions, molecules are in the ground electronic state, but not in photochemical reactions. With luminol, a molecule is formed which is already in an electronically excited state. When this molecule returns to its ground state, light is produced.
Some dyes have been added. From left to right:
1. No dye
2. Fluorescein
3. Eosin Y Disodium Salt
4. A Mixture of Both Dyes