London weather conditions have not been good for testing the blinds under all conditions as can be seen from the graph above.
There is a strong correlation between the internal and external light readings giving a straight line response (y=0.035x) under diffuse sky conditions. This means that for overcast conditions, our testcell behaves like a near perfect integrating sphere.
Under clear sky it can be seen that there is a fall in the light level entering the testcell. In this case it is most likely to be a function of the reveals or the geometry of the cell. The two peaks in the image on the right-hand side are due to misalignments of the shading ring and a possible reflection. Mirrors were added to the revelals to remove their affect.