The use of light within writing can offer information. Used correctly, it can show time, a presence, a warning....
Use light to describe: (for example if sunlight comes from the east we know it's morning, dew glistening on the branches will further confirm time of day without telling the reader it is morning).
A line of trees
A mountain range
Now, rewrite the same scene with light coming from a different direction. It doesn't have to be the same source, but it does need to be light.