In my office though, I experimented with a pair of Ikea mirrors for more interesting light play. They’re mounted face up about 9″ down from top of glass, comfortably above eye level. The underside is painted white, to serve as a mini “ceiling” to the light reflected up from the venetian blinds below.

Mirrored light shelves reflecting sunlight onto ceiling

My office ceiling is the underside of a 12-in-12 pitched roof; the exposed surface is a dark grey polyiso insulation with merely a thin coat of white primer. Even so, the reflected sunlight on a clear day (center image, below) is roughly 2.5 times brighter than a pair of T-8 fluorescent tubes (right). Compare this to the ambient light of the ceiling — from light shelves reflecting the surrounding sky (left). Note that readings (in footcandles) are taken 12″ from the ceiling to isolate the light source for the meter.

Light readings for ambient, reflected sunlight, and dual T-8 fluorescents

In another project I inverted the concept, reflecting low winter sun down through skylights. Here the reflectors act to shade the skylights during the summer months. Specifics of this project are spelled out here.

South-facing, inverted reflectors over skylights to catch winter sun

For retrofitting windows, an interesting product called LightLouver based on the same principle as the light shelf has been developed as a vertical window treatment. I haven’t seen this in person, though, and don’t know how it compares to a standard polished chrome venetian blind.