Light tubes:

http://www.solatube.com/

http://www.solatube.com/

Light tube is a structure in order to use renewable energy in commercial and residential areas. This structure has simple structure that could be easily installed on any kind of roof to catch sun light and bring it inside the building. Light tubes usually are used in part of the house that does not have window like kitchen,bathroom and laundry room. Furthermore they can be installed in warehouses . A light tube consisted of a dome on top of it,a tube with mirror inside of it for light reflection and a lens to make sun light softer. In my opinion his simple technology could be so efficient especially in big commercial buildings and warehouses. The cost of each light tube is not expensive and it does not take so long to pay itself . Furthermore it is a natural light that could be more pleasant for people.
Source: http://www.solatube.com/