Nokia used to have this, and they recently added it to their newer Lumia models, called "Glance". It's cool, can show time, wallpaper and notifications.
Example image: http://www.wpcentral.com/sites/wpcentral.com/files/styles/la...
Example image: http://www.wpcentral.com/sites/wpcentral.com/files/styles/la...
My Lumia 920 has IPS LCD, so it need to backlight the entire screen. But still, the energy consumption isn't that high. It turns off the screen when in the pocket. I have more than enough juice left at the end of the day.