The sun is the dominant source of light for the Alternate.
Photo Augmentation is a more specific use and individual power of Photokinesis. Unlike photokinetics, however, these people are unable to generate light in their own bodies or act as their own source. They literally require light for their powers to work. This means that in order for the ability to function properly, continued exposure to light is required.
Photo Augmentation is largely a form of photosynthesis, by which light is absorbed photochemically. This heightens their strength, speed, reflexes, metabolism, and acts as a source of renewable chemical energy. These enhancements are, of course, dependent on light available. The power also seems to increase durability proportionally to prevent the body from succumbing to the increased forces of the ability.
The peak for this power would be while bombarded by photons, offering a near infinite source of energy. The Alternate is seemingly capable of storing light within their body in order to utilize their powers during periods of darkness. It is possible to use these abilities at night but to a restricted degree due to the lack of a renewable light. Thus, any use of their power at night would be negligible and disappear after prolonged use, though it could remain stored indefinitely until utilized for enhancements. If the Alternate were trapped in darkness with no source for recharging their energy, all their enhancements would become inert.