Not all light is the same

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.