Fig. 3. a) Sketches of our 15- by 30- and 30- by 60-cm test cells in plan and cross-sectional views (not to scale). Each of the textured glass plates is separated from a 19-mm (3/4") glass plate window by a thin rectangular gasket. A needle inserted through the gasket allows pressurization of the intervening space, pushing the two textured plates into close contact. Note that a larger number of bolts than shown were used to assemble the 30- by 60-cm cell. (b) Sketch of our test stand (not to scale). Light intensity is controlled through a feedback circuit. The light box also contains a cooling system to prevent warming the experiment.