This is a purely geometric-based solution of light emitting from a source and spreading out in all directions and contacting another sphere some distance away. This does not account for any fancy "scientific" stuff that I am no expert at, such as the energy getting absorbed by the Earth’s atmosphere, or other factors that may be at work in this matter.
Here are some other sources I found that address some of the scientific issues of this matter, as well as other mathematical approaches to estimating this value:
https://www.quora.com/What-percent-of-heat-from-the-sun-reaches-the-earth
https://web.extension.illinois.edu/world/energy.cfm
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Step 1 Surface area of a sphere: A = 4πr^2 r is the distance of the Earth from the Sun = 92,960,000 miles (92.96 million miles) Surface area of the "sphere" formed by this distance: 12Area = 1.09×10 ^ 17 square miles
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Step 2: Cross-sectional area of a sphere: A = πr^2 1234r = radius of earthr = 3,958.8 milesA = 4.92×10 ^ 7 square miles
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Step 3: Divide Area of Earth by Area of Sphere: 1234(4.92×10 ^ 7) / ( 1.09×10 ^ 17 )= 4.5137615e-10 = 4.5292×10^-10For reference, "1 Billionth" is 1e-9, so 4.51e-10 is even less than this… Basically, it’s "Less than 1 billionth" It could also be stated as 4.5 "10 billionths" 12= 0.00000000045137615 = 0.000000045137615 %
