The output of sun is heat and it reflects to us in the form of rays. Isn’t it? But you all have something more to know about, that will make you feel surprised and understand how efficient the sun actually is! Sun is actually a star which contains three part of hydrogen in its nature size and the remaining one art is filled with helium. Hydrogen is the main reason behind the heat that is produced by the sun . How? you all know that well and am not going to bore you with detailed explanation. So, i make it simple. Collision of Hydrogen atoms, forms into helium and during this collision a very high amount of heat is produced. Are you clear about it now? Now, proceeding further, a practical thought- When the sun makes you feel more hot than the normal way how it used to be, then it means that many number of collisions are taking place in the sun , that is, process of conversion of hydrogen as helium.