ILLUMINANT INVARIANT CALIBRATION OF THERMOCHROMIC LIQUID-CRYSTALS

A video-based system is described for using thermochromic liquid crystals (TLCs) to make highly accurate, full-field, surface temperature measurements, independent of the illuminant spectrum, background lighting, angle of incidence, and optical path. The system is comprised of three parts: (1) mixing, filtering, and spraying protocols that produce uniform TLC surfaces; (2) on-axis, cross-polarized primary lighting; and (3) correction algorithms for the optical path, the intensities, and spectra of both the primary illuminant and the background lighting, based on CIE Illuminant C-referenced color specimens placed in both the application and calibration fields of view. When 30 frames (1 second's worth of data) are averaged, the uncertainty is less than +/-0.25-degrees-C (with 95% confidence) even in the presence of various combinations of sunlight and fluorescent/incandescent room lighting, as long as the viewing angle is within +/-25-degrees of the normal.