These play an important role in resetting your circadian rhythm properly. They emit blue light directly onto your retina to wake you up. They need to be worn for the allocated time only, to ensure that your sleep for that evening is not affected.
They need to be worn for 20 mins in the morning. This ensures that blue light goes directly into your eyes, in order to set off the 'cortisol' response to wake you up. These glasses are especially useful when travelling and waking up in different time zones.