The formation of C-C covalent bonds in carbohydrates from the products of light, which are primarily ATP and NADPH, is a complex process that involves several steps and multiple enzymes. This process, known as carbon fixation, is a key part of photosynthesis.

Here's a simplified overview:

1. Light-dependent reactions:

* Light energy is captured by chlorophyll and used to split water molecules, releasing electrons and generating ATP and NADPH.

2. Carbon fixation (Calvin Cycle):

* CO2 from the atmosphere is incorporated into a 5-carbon sugar molecule called ribulose-1,5-bisphosphate (RuBP). This reaction is catalyzed by the enzyme Rubisco.

* The unstable 6-carbon intermediate quickly splits into two molecules of 3-phosphoglycerate (3-PGA).

* ATP and NADPH from the light-dependent reactions are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P).

* Some G3P molecules are used to regenerate RuBP, continuing the cycle.

* Other G3P molecules are used to build glucose and other carbohydrates.

Key points:

* The process of forming C-C bonds in carbohydrates is not a direct result of light energy. Instead, light energy is used to produce ATP and NADPH, which then provide the energy and reducing power needed for carbon fixation.

* The Calvin Cycle involves a series of complex reactions, each catalyzed by a specific enzyme.

* The overall reaction can be summarized as: 6CO2 + 6H2O → C6H12O6 + 6O2.

This process is essential for life on Earth, as it converts inorganic carbon into organic compounds, providing the basis for the food chain.