This is a 2-Leaf Barndoor Set for the Mole-Richardson 46" long Biax 8 Tube fluorescent fixture.
Barndoors narrow the beam spread of a light fixture. They help create a 3-dimensional look to a lighting scheme by placing light in a specific area or by keeping it away.
The more leaves a barndoor set has, or the longer the leaves, the more precisely the beam can be controlled.