Im not arguing against you here or anyone on this post but photosynthesis has two cycles both which create ADP and NADPH, which are important necessary steps in the growth of all vegitation.
Carbohydrates arn't the endpoint of energy just a step in the process, plants are able to produce energy in many many different ways. The end point is broken down into a few different types of energy, most common being ADP and NADPH in plants.
"Light reactions need light to produce organic energy molecules (ATP and NADPH). They are initiated by colored pigments, mainly green colored chlorophylls.
Dark reactions make use of these organic energy molecules (ATP and NADPH). This reaction cycle is also called Calvin Benison Cycle, and it occurs in the stroma. "
http://www.eschooltoday.com/photosynthesis/dark-and-light-reactions.html
I have about 5 chapters on it in my botany textbook but here's a rough and easy breakdown in this link.
Again not trying to be an asshole, just inform. You asked It has been delivered.
The important thing that we need to look at here with cannabis is the main outcome that we want. Typically during vegetative growth the reason you can do 18/6 or 24/0 is because you want as much of that active light reactions to build carbohydrates in the plant that allow the plant to grow stronger, thicker vegetative parts to eventually hold up to the strength of the flower. we switch to less light during flower for a few reason, simulate nature and change in season which initiates different cycles within the plant giving the plant the energy and process start ups required to flower. And to allow for the plant to "breathe" One of the main purposes of plants fruiting before the end of the light season is to allow the plant to complete its grow cycle before its natural death through the season. Less light doesn't mean less energy for the plant its just a different energy. With cannabis you need a combination of light and dark for the buds, the flowers will tend to grow heavier during the evening during the CO2 release of the plant. (Yes plants breathe) This release process happens most strongly through flower sites on a plant which pushes nutrients and energy along with it through to the flowers of the plant. The light cycle is required to keep the plant strong and alive to allow it to bear its beautiful fruits. Most people commonly use 12/12 during flower for cannabis because its been proven practice works. Different strains, phenotype, environment and grow methods. can lead to either longer or shorter light spans during flower.
All plants need day and night cycles, they need to breathe and express the energy from the leaves and roots to the fruits and flowers.
Simplified: Day produces more energy than night for most plants, however during the day that energy is mostly stored inside the leaves and roots. During night the plant "exhales" and goes through different photosynthetic processes that transport the energy stored throughout the plant to the important and new growth areas on the plant.
edit: "ways"