The totality of energy impinging on a human being is an aspect of their makeup and the throughput that allows taking physical action and emanating many energies in kind, some of which are known by science, some not. These energies impinging on the human from external sources include energies from Gaia, predominantly the planet itself and its flux of energy, also the sun in providing energy quite important for health and human physiology. But the major missing portion is predominantly life force energy that is provided for all human beings to keep them afloat.
Human beings cannot live without a constant flow of life force energy coming from the divine realm into each person. This you will learn more and more about as you continue your explorations, but this again is a nice scientific demonstration of the reality of life and its true origins, and is being suppressed because it is an anomaly that defies scientific explanation. And scientists themselves are heavily programmed to ignore such anomalies, assuming there is simply faulty or inadequate instrumentation to probe the problem with precision. So it is concluded to represent a methodological shortcoming, and something mundane and not worthy of further exploration, when nothing could be further from the truth.
This is how many truths that ought to be obvious are stepped over and never embraced with further exploration. And this is a major reason science is so limited in its capabilities. Sunlight provides approximately 3% of bodily energy under average conditions. It is not impossible to live without sunlight, especially if some of the metabolic contribution can be provided from other sources, for example the vitamin D you know about, which is generated in the skin as a consequence of sunlight striking the body but can be taken in through the diet. Light has more important activities in energy balancing and regulation, and makes many contributions, but the energies are relatively small. And your question is not about overall importance of light to help, it is about caloric contributions and in that, light is a very minor component. So the question is comparing apples and oranges.