Light penetrates past the eye and the skin, to your body and brain. It is nourishment (vitamins!), it affects your body temperature, rate of respiration and hormonal levels. It is our time keeper, keeping us in sync with daily and seasonal rhythms. It can wake you up or soothe you, stop you from sleeping, or keep you alert.
We humans evolved in daylight -- natural light. One key to understanding natural light, and its effect on our neuropsychological system, is to understand that sun light is always changing, always moving, no matter how imperceptibly. Its color and its angle are constantly shifting. Cool in the morning when it is rising in the sky, yellow/white in the midday (when it is above us), hot rose in the later afternoon, as it lowers in the sky, lavender in the early evening. It is this play of light that gives natural light its character, and triggers our body brain system.
Artificial light is light made by humans to supplement daylight, or to replace it when it has left the stage. No single bulb can be said to share all the qualities of sunlight. You can’t buy natural light.