Using a similar setup to the previous posting different filtering methods have been used to see if pentration depth can be tested.
In test 1 a heat sink was placed in the tube preventing any visible light entering the water. The stable temperature of the heatsink was 100C The tube was ventilated from just above the transparent seal above the water to just below the heatsink. at the top of the tube. The bulk of radiation entering the water would be radiated from the bottom of the heatsink
In test 2 the heat sik was replaced with a 1cm deep tray of water. This should effectively remove any LW IR leaving only visible light. The tube was again ventilated.
The temperature plots with depth are shown together with the rate of change of temperature with depth.
Not very conclusive although it appears that 100C blackbody is significantly attenuated below 6mm of depth. (the final 2 thermocouples showing the leakage of the thermos heating the water (possibly)
The visible light seems to be adding significantly to the water at a depth of 55mm.
Note that there seems to be no explanation for the dips in reading of temperature. The apparatus was not disturbed and no light change occurred. (one of the dips - at 24mins was caused by the filter water being replaced with cool water)