In the photomicrocalorimetric module designed by Johansson and Wadsö for a commercial Thermometric TAM heat conduction batch
microcalorimeter, the incident light from an external xenon lamp was divided by a beam splitter and directed to the two vessels
of the differential system by light guides ideally to give zero heat flow. In practice this proved difficult and so to improve
the balance between the vessels in terms of the incident light heat output as well as potentially to give more versatility
regarding the choice of wavelengths, the xenon lamp-based system was replaced in the first stage by a pair of cold white LEDs
embedded directly in the test and reference vessels. The LEDs had independent electrical circuits to achieve the balance by
manual adjustment. As a second stage, the test vessel was equipped with PTFE tubing for changing the liquid phase in it while
it was in the middle thermal equilibrium position. This improved the reproducibility of the results.