Tried the 30 cm styrofoam ball and got some more measured lumens, 1095 to be exact. This is 1,7 % higher than with the 20 cm sphere.
Some comparisons with different integrating spheres I’ve tried.
The 30 cm sphere has a sanded (1200 grit paper) inner surface. On both spheres the measurement is done on the surface. Thanks to djozz for the idea here Integrating sphere #4 (the fast and cheap one)
In my sphere the flashlights rests on top of a transparent plastic sheet level with the inner surface.
