The part of photosynthesis where energy from the light reactions is used to make simple sugars is called the Calvin cycle, also known as the light-independent reactions or the dark reactions.

Here's a breakdown:

* Light reactions: These reactions use light energy to produce ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These molecules are energy carriers.

* Calvin cycle: This cycle uses the ATP and NADPH generated in the light reactions to convert carbon dioxide from the atmosphere into glucose, a simple sugar. This process is called carbon fixation.

So, the Calvin cycle is where the energy from the light reactions is utilized to create the building blocks for plant growth and energy storage.