FRPFR | o | Light going thru two parallel right lenses in theater direction is not much attenuated, at least not much more than one lens, but it is given a slight orange hue ('o'). A single lens does not color the light. |
FRTFR | b | The same lenses when turned give a slight blue hue ('b'), yet little attenuation. |
FyPFz | o | Both lenses do the same, even mixing left and right. |
FyTFz | b | ditto. (4 cases) |
ByPBz | o | I think thermodynamics requires this considering FyPFz. |
ByTBz | b | ditto (no one way mirrors) |
xyPxz | o | In general (8 cases) |
xyTxz | b | ditto |
FRPBR | c | Light travels thru second lens backwards. The hue is gone ('c') “clear”. Very little additional attenuation. |
FxPBy | c | four cases here. |
FxTBy | 0 | Black! only a percent or so of blue light gets thru. Notice so far no distinction between left and right lenses! |
BxPFx | c | clear again if we match lenses. |
BxPFy | p | dark purple if x≠y. Perhaps 20% of light gets thru. |
BxTFx | 0 | black again as for FxTBy. |
BxTFy | c | Very clear if x≠y! no coloration. |
I am confused!
Further experiments would involve a mirror which I think I understand!