Though it’s not a genuine photosynthesis, an energy plants get even without consuming anything, we could remember our daily cycle and regulate our biorhythm through sunlight.

“Human photosynthetic cells” exist in the eyes of humans. They are called ipRGC (photoreceptors). These cells are most sensitive to light, specifically in the range of 480nm wavelength. The 480nm wavelength of light through the eyes is absorbed by a protein called Malanopsin in photoreceptors and regulates secretion of melatonin in the connected brain, well known as sleep hormone. Is it too complicated? For more information, take a look at Lab Note