When light strikes chlorophyll molecules, they lose electrons. The left over electrons are donated to chlorophyll. It carries high energy electrons and hydrogen from the light-trapping reactions to the Calvin Benson cycle. The Calvin Benson reactions do not require light and yet they usually do not occur at night. These are unstable molecules that can t be stored for very long.
Photosynthesis requires carbon dioxide which enters plants through stomata.
But when stomata open to let in carbon dioxide, plants lose a lot of water. Many desert plants are CAM plants which have devised a way to open stomata at night. Their roles are similar in that they act as carriers of high energy electrons that can be used to do work, and hydrogen atoms. NADH donates electrons in the electron transport chain in mitochondria which ultimately helps to make ATP molecules. They ultimately become part of sugar molecules.