Spectral distribution of intensity means the strength of light at different colors (or frequencies). For example, if you shine a flashlight on a wall and then shine a rainbow on the same wall, you'll notice that the colors of the rainbow are much brighter and stronger than the light from the flashlight. The colors of the rainbow are spread out and each color has its own intensity, which is why they look so bright and beautiful. Scientists use the spectral distribution of intensity to study light and figure out what it's made of, and how it behaves.