How do plants grow toward light sources naturally?

Plants grow toward light through a process called phototropism, which is controlled by a hormone called auxin. When light hits a plant from one side, auxin redistributes away from the illuminated side and accumulates on the shaded side. This higher concentration of auxin on the darker side causes those cells to elongate faster than the cells on the lit side, which bends the stem toward the light source. The photoreceptors responsible for detecting light direction are called phototropins, which are sensitive primarily to blue light wavelengths. This response allows plants to maximize their exposure to sunlight for photosynthesis. The same auxin-based mechanism also explains why plants in windowsills gradually lean toward the glass over time.