With the advent of very high resolution satellites in the last decade or so, the conventional ideas in remote sensing are undergoing a rapid change. High-resolution imaging satellites working in the optical and NIR bands are increasingly being operated even in night-time, not to study the thermal emitted IR, but the artificial light sources by humans. In the past decades, the US Defense Meteorological Satellite Program (DMSP) satellites have been used for night-time imaging of man-made objects and features, albeit at a low resolution. Imagesat International offers high-resolution night-time imagery through its EROS-B satellite. NASA provides a nice world map of night lights, which shows hubs of activity at night on the Earth. Chris Elvidge of NOAA is a well-known name in the study of night-time Earth, and here is a great feature article on years of research done by him. For some more awe-inspiring night-time images, see NASA’s Earth Observatory Night Lights feature page.
Skybox Imaging is now delivering high-resolution images and video, both at day and night-time. Take a look here.