Here's why:

* Photosynthesis: This process is how plants create their own food (glucose).

* Light Energy: Plants absorb light energy from the sun using chlorophyll (the green pigment in leaves).

* Conversion: This light energy is then converted into chemical energy stored in the bonds of glucose molecules.

So, while plants use water and carbon dioxide as raw materials for photosynthesis, light is the ultimate source of energy that drives the process.