How reducing sunlight would affect Earth.

ozone in earth's upper atmosphere blocks much of the UV

The sun affects earth by its sunlight. If there was no sunlight there would be no life on earth. The sun can influence the earth's environment in a variety of ways and on different time scales. The Sun does much more than this. If there were no sun, the Earth would be just another rock in space. If the sun had not provided its gravitational field, the earth might have flown into another star somewhere off in space by now. The Sun does give us heat, which we need to live, and light, which plants need for photosynthesis. The sun also produces the light which is reflected by the moon, which lights our night sky. A rotation around the sun is the measurement for an year.

Hope I helped.