The main objective in excluding light is that of reducing the amount on a screen to a minimum of one-tenth foot candle, ... Many teachers darken classrooms in which they teach by pulling down the WINDOW SHADES, which were originally installed to control the distribution of light. ... If OPAQUE SHADES are used, it is usually necessary to install extra frames with face boards or flaps over the edges of theanbsp;...
|Title||:||Audio-visual Materials and Devices|
|Author||:||Benjamin Franklin Holland|