David Lowell loved working with plants, that was his one true love. When he did further study on the process of photosynthesis he discovered that he could harness that into photogenesis, which would use the same process but on a human. He was working at Osborn Industries. After making this discovery he ran into Norman Osborn's office and showed him then demanded a raise. Norman was still under the side effects of the new Green Goblin serum and instead of giving Lowell a raise, he shut down his lab. Lowell went to his lab and then consumed the formula, transforming Lowell for ever.
Sundown has the ability to draw and absorb the solar radiation from the sun which he can harness into potential class 100 strength and durability, solar energy projection, sub-sonic flight, rapid growth (estimated around 50 ft), near instantaneous healing, and some teleportation (limits unknown).