Radiation is created from the conversion of hydrogen into helium in the Sun's core. As the Sun ages, the amount of helium deposited in the core increases and the output of solar energy becomes brighter. In around 1.1 billion years, the output of the sun will have increased by 10%, and in 3.5 billion years, it will have increased by 40%. This level of solar radiation will be powerful enough to boil the oceans on Earth, though earlier levels sill have heated Earth's water and atmosphere sending them out into the atmosphere making Earth uninhabitable for humanity. Hopefully, in the meantime humans will have colonized the outer Solar System and beyond while planets further out from Earth will be experiencing enough solar radiation to become habitable after terraforming. In around 7 billion years, the Sun will run out of fuel, become a white dwarf, cool and come to the end of its life.
The Sun is about 4.57 billion years old, having formed during the creation of the universe from swirling gas cloud. As the result of a supernova shock wave, the gases collected together and collapssed under its attractive gravity. The greatest concentration of mass collected in the spinning center where accumulating heat and gasses pulled inward from the edges eventually ignited a nuclear fusion reaction. The Sun puts out solar radiation because of this nuclear reaction, which includes visible light and many other frequencies of radiation.
In about 1 billion years, the sun will be 10% brighter because more helium is being created at the core, causing the sun to burn more hydrogen. This increases the energy output and causes the sun to be brighter.
In about 3.5 billion years, the sun will be 40% brighter. This will prevent any life on Earth because it will cause oceans to boil and ice caps to melt.
Essentially, the energy is increasing over billions of years causing the sun to lose water vapor and become dry.