Einstein made sense of their data with his theory of special relativity. In Maxwell's wave model the color of light depends on its frequency, the brightness on its amplitude. Electromagnetic waves are created by accelerating electric charges, The electromagnetic waves then exert forces on the electric charges causing them to accelerate. More on the Maxwell model of light. Blackbody Radiation Hot objects emit light.
Hot objects glow red, they are red hot.
Turn on an electric hot plate, or heat a nail in the flame from a torch and notice the color of the glow that results. As the plate and the nail heat up the color goes from deep red to orange to yellow, heat it enough and it would become white. Planck was able to explain the color of light emitted by hot objects by modeling energy as existing in discrete chunks, quanta. Albert Einstein Explained the photoelectric effect by extending the idea proposed by Planck. He suggested that light energy was quantized.