Experiments in Fluids

, Volume 43, Issue 6, pp 929–937 | Cite as

Angular effects on thermochromic liquid crystal thermography

  • Paul M. KodzwaJr
  • John K. EatonEmail author
Research Article


This paper directly discusses the effects of lighting and viewing angles on liquid crystal thermography. This is because although thermochromic liquid crystals (TLCs) are a widely-used and accepted tool in heat transfer research, little effort has been directed to analytically describing these effects. Such insight is invaluable for the development of effective mitigation strategies. Using analytical relationships that describe the perceived color shift, a systematic manner of improving the performance of a TLC system is presented. This is particularly relevant for applications where significant variations in lighting and/or viewing angles are expected (such as a highly curved surface). This discussion includes an examination of the importance of the definition of the hue angle used to calibrate the color of a TLC-painted surface. The theoretical basis of the validated high-accuracy calibration approach reported by Kodzwa et al. (Exp Fluids s00348-007-0310-6, 2007) is presented.


Liquid Crystal Spectral Reflectance Color Component Viewing Angle Thermochromic Liquid Crystal 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols


charge coupled device


blue component value


referring to black reference


arbitrary constant


green component value


integer value


maximum value


minimum value


measured voltage


number of calibration curves


index of refraction for air

\(\overline{n}_{\rm TLC}\)

average index of refraction for TLC


initial conditions


hue angle


red component value




region of interest




partial saturation


time required to collect calibration curves (h)


Thermochromic Liquid Crystal


voltage or color parameter (Hay and Hollingsworth 1996)


color parameter (Hacker and Eaton 1995)


referring to white reference


spatial coordinate


spatial coordinate


channel value




minimum cell size in x-direction


minimum cell size in y-direction






difference between mean component values


angle of illumination


angle of scattering or viewing


wavelength (nm)


wavelength of maximum scattering for normal incidence and observation (nm)


time necessary to convert \({{\mathcal{Z}}}\) for each pixel (s)


time necessary to set temperature of calibration surface (s)


number of pixels in a given ROI



This research was sponsored by General Electric Aircraft Engines, through their University Strategic Alliance Program. The first author received support from the National Science Foundation via a 3-year Graduate Fellowship. The authors would like to express their sincere gratitude to F. Buck, B. Bergholz and D. Wisler (at GEAE) and D. Dods (at Instrument Technology Incorporated) and V. Davison at (QC/NDT) for their assistance and advice in the course of this experimental program. S. Carver, J. Hammer, J. Glassman, T. Hasler and L. Johal are gratefully acknowledged for their high level of expertise in manufacturing various parts in this experimental program.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Mechanical Engineering, Flow Physics and ComputationStanford UniversityStanfordUSA

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