https://design.tutsplus.com/articles/improve-your-artwork-by-learning-to-see-light-and-shadow--cms-20282
https://www.pinterest.com/ejunguenet/light-direction-for-painting/
https://www.pinterest.com/lloydthibodeau/drawing-painting-sun-rays-in-forest/
https://www.google.com.vn/search?q=understand+light+direction+in+paintings&espv=2&biw=1366&bih=676&tbm=isch&imgil=xDfMZVJQNahuqM%253A%253Bjf9pcqVSgJjARM%253Bhttps%25253A%25252F%25252Fwww.pinterest.com%25252Fexplore%25252Fstill-life%25252F&source=iu&pf=m&fir=xDfMZVJQNahuqM%253A%252Cjf9pcqVSgJjARM%252C_&usg=__6CFMmdNHNUZTQETwwSciarOriv8%3D&ved=0ahUKEwiplYqm3v7QAhUHR48KHdeiAx0QyjcILQ&ei=WwZXWOn7IYeOvQTXxY7oAQ#imgrc=xDfMZVJQNahuqM%3A
