Answer:
light and dark values are used to create mood because values can have psychological influences on the brain and automatic emotional associations as well as being socially universal due to it often matching real life lighting and colors.
Explanation:
for example, if one were to create a joyful mood, they would create a bright scene with light and saturated or pastel values because often light symbolizes positive or energetic aspects, while dark values often symbolize negative, low energy, or simply moody feelings, like a picture of a cafe at night being much more mellow with its dark values compared to a brightly colored cafe at day.