During the dark, levels of the hormone leptin (hunger control), go up. This means we do not feel hungry while low levels make us hungry.

Ans research found that sleep disruption and turning on lights lowers leptin levels which makes people hungry in the middle of the night.

Some kinds of light make you more alert and more awake, and others have less of an effect:

• Sunlight is strong in blue, short-wavelength light, although it includes all other colors as well. That’s important in the morning when we need to be alert and awake.
• Your tablet, phone, computer or compact fluorescent lamp (CFL) all emit this kind of blue light. So they are dangerous if used at night.
• Other kinds of light, like dimmer long wavelength yellow and red light, have very little effect on this transition.

• Before electricity, people experienced bright, full-spectrum days of sunlight and dark nights. We slept in a different way than we do now.
• Everything changed when electric lighting was invented in the latter part of the 19th century. Since then there has been an ever-increasing assault on dark.
• Today, most of us get too little light during the day and too much at night for our circadian rhythm to function at its best.