Perhaps Leonardo da Vinci had learned from this observation that the believable existence of an object or its identity depends upon the crucial element of light and no light just as its color and texture and odor and so on. And this shadow can be diminished if the light comes from within.
The forms of bodies could not be understood in detail but for shadow -Da Vinci
A man of unquenchable curiosity and a voracious appetite for knowledge made him an outstanding personality of the Renaissance era agreed by most as the universal genius. It were his hands that bestowed on a popular panel the magnificent and mysterious smile of Lisa del Giocondo which made her the Mona Lisa of today: an invaluable ornament in the treasury of visual art. It was his wisdom that captured the sweetest moment of affection and service to mankind just before love betrayed, baring the naked truth that some are bound to be lost as seen the philosophical painting of 'The Last Supper'.
His highly innovative and ingenious mind engineered craftsmanship into his creations such as the Flying machine, Parachute, Armored car, 33-barreled organ, Giant crossbow, Robotic knight, Scuba Gear to name a few. His inventions and designs were unfathomable to the scholars of his time. I personally find his 'self-propelled cart to be the most intriguing: an independent cart which does not require the whip of a master.
He believed that the intentions of man could be studied through his gestures and motion and this understanding for Leonardo became the arch between the shores of science and art for gestures and expressions require movement of flesh and bones. This made him an earnest anatomist as seen through his sketches. His 'Vitruvian Man' and his study of fetus in a walnut shaped uterus are his symbolic drawings in which the former shows a well proportioned masculine physique in thrall to the measuring line of nature and the latter representing a seed with potential of growing and bearing much fruit.
He, by placing layers upon layers of glazes brought a life-like luscious silken finish to his paintings. He also developed a technique called 'Sfumato', giving his paintings, 'Mona Lisa' and 'Salvatore Mundi' a more sophisticated look. And as I mentioned earlier, his inventions and designs baffled the scholars of his time: this makes us question what was Leonardo in search of? For him, science and art weren't two different things or fields but they were like two arms belonging to the same body. He was only looking for a bridge that connects them. A law that connects everything we feel, touch, hear, see, perceive and judge around us and probably learned if there is light, there is shadow; if there is a crest, there is a bottom; if there is birth, there is death and all in between is more like a dream.