Light and heat are just two forms of electromagnetic radiation emitted by the sun. This energy is caused by nuclear reactions in the sun which cause it to make electromagnetic energy of all wavelengths. The sun is really just a mass of hot gasses that explode with energy in a way very similarly to a nuclear bomb. However in the sun, the explosions never stop. Each second the sun changes about four million tons of its mass into heat and light energy.
Solar energy radiates through space to the Earth.
Some of the wavelengths are absorbed, scattered or reflected back into space by the Earth's atmosphere. From there it is either absorbed or reflected back from the Earth's surface or from clouds. This reflective radiation is measured by remote sensing instruments. Scientists have made charts that show the characteristics of the electromagnetic wavelengths. Some of the energy radiation, or rays, of the sun we feel as heat, some of them we as light, and some have to be detected with special instruments.