A comparison of trichromic systems for use in the calibration of polymer-dispersed thermochromic liquid crystals

Samples of polymer-dispersed chiral nematic liquid crystal with different active temperature ranges were calibrated using four different trichromic representations of the liquid-crystal color. Three of the representations were hue-based, and the fourth was a simple linear regression. The comparison was done using commercially available imaging equipment. The primary criteria were the effective width of the calibration range and the resulting uncertainty in temperature. The results characterize the calibration range and uncertainty that can be expected from careful use of a typical thermographic system employing the selected liquid-crystal product and the selected colorimetry techniques. A dimensionless temperature was defined that collapsed data from all the samples to a single calibration curve. Introductory discussions on the thermochromic behavior of liquid crystal compounds and on the colorimetry theory that underlies quantitative thermography are also included.