Thermochromic printing inks change color in dependence of surrounding temperature. This color change occurs inside the microcapsules containing thermo-responsive materials. There are two basic types of thermo-responsive materials; leucodye-based composites and thermochromic liquid crystals. Liquid crystal thermochromic printing inks start a color change at the defined activation temperature (TA), but the color change occurs in several degrees wide region above the TA. The color change temperature range is called activation region but can also be called "the color play interval". Outside the activation region this kind of printing ink is colorless. Within the activation region the color changes throughout the whole visible spectrum from red, orange, yellow, green, blue to violet, the effect known as "color play". Within "the color play interval", the spectral color with given wavelength λ appears when the elongated molecules of the active material inside the microcapsules develop a helical superstructure with pitch equal to λ. As the temperature raises the helical pitches shrink causing the shift of the peak in the reflectance spectra towards shorter wavelengths, therefore the color of the material changes towards blue shades. Thermochromic effect of liquid crystal thermochromic printing inks is a result of temperature dependent helical pitch. Temperature dependent optical effect achieved by liquid crystals is quite different from conventional printing inks and thermochromic leucodye-based printing inks and is explained in detail in this research. Special conditions are needed to observe and measure the colors of printed liquid crystal thermochromic ink samples. The presented research is focused on optical properties of water-based liquid crystal printing inks, screen-printed in several ink layers on various types and colors of printing substrates. The characterization of optical properties is determined by spectroscopic measurements. The "color play" effect was quantified by spectral reflectance applying (45°:0°) and (8°:di) geometries. The measured temperature dependent iridescent colors were calculated and presented as CIELAB colorimetric values, showing the "color play" effect throughout the visible spectra. The results show that liquid crystal thermochromic printing inks reflect incident light in a rather narrow spectral region. The temperature dependent iridescent colors are seen very clearly when the ink is printed over black background, while on the white substrate is hardly visible.This research shows that thermochromic liquid crystal printing inks reflect the light by spreading it in a way that the (45°a:0°) measurement geometry cannot capture the entire color play effect. This is an important practical message as this geometry is commonly used for spectrometric evaluation of samples with no angular dependent effects, i.e. for samples whose color is based on the absorption of light. The problem was solved by integrating sphere accessories, which collect (spatially integrate) the radiant flux reflected by the sample. The best results were obtained by larger diameter integration sphere. Communication mechanism has been designed specifically for liquid crystal thermochromic printing inks based on their temperature dependence. The proposed mechanism enables the analysis of the active thermochromic material without any colorimetric influence of printing substrate or applied printing ink layers. In the research special attention is devoted to stability of the samples printed with liquid crystal thermochromic printing inks. According to the available literature, the stability of this kind of printing inks has not been evaluated yet. The samples were exposed to daylight for varying time periods. The samples were also exposed to defined light and temperature conditions in a special laboratory climate chamber. The changes of the dynamic color due to light exposure were measured resulting with poor dynamic color stability. Temperature dependant optical properties of liquid crystal thermochromic printing inks enable their usage in various fields of application. The presented application examples, in conjunction to performed measurements can contribute to faster development of new kinds of indicators based on liquid crystal thermochromic printing inks, in the areas of functional packaging, security printing and others.