Thermochromic (TC) liquid crystal inks reflect incident light in a rather narrow spectral region, which is caused by selective reflection of light on chiral (twisted) molecular structure. The reflected light produces iridescent colour which is continuously shifted from red to blue part of the spectrum with temperature. This is special type of TC effect: instead of selective spectral absorption, which is usual for all conventional coloured inks and also for leuco dye-based TC the effect is based on reflectance of a narrow band within visible spectral region. The effect is best observable when the ink was printed on a black surface. Collimated illumination and collimated detection does not allow recognizing the effect; the integrating sphere measurements are required to quantify the colour in dependence on temperature. The position of the reflectance band shifts exponentially towards shorter
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