Due to an energy crisis at the time in the late 1970s, heat was very costly and so the school department needed to find ways to conserve on heat. As a result, the large glass windows were removed and replaced with insulated panels, leaving only the very small top and bottom glass uncovered. This kept in heat, but also made the school darker without the large glass windows.
The insulated high school building with most of the glass removed (1982 top, 1985 bottom).
Photo from old yearbooks