We found that any uniform stressed area in loaded birefringent material
observed in a polarized, dispersed light shows an extinction effect (black
fringes) for different light wavelength A. The shape, speotral position of
the fringes and their number depends on value of the stress.
The analysis and explanation of the effect were done. The laboratory,
computer aided spectrometer was build for making precise measurements for
different loading conditions; the results of the measurements are described.
The application of the effect as an uniaxial force sensor is proposed.
Photoelastic sensor with fringe image transfer by an image-guide to a computer for stress analysis was constructed for those applications where the place of measurements is hard to reach and electrical instruments are not permissible. Two types of sensors are presented: one, disc-like, for uniaxial stress observations and the second one, called a hollow glass cylinder, with axially bored stress concentrator for biaxial stress measurements. Sensor is a central cylinder glass cemented in a cubical concrete block. The sensor is connected to autocollimating polariscope, which allows the sensor to be lit and transport an isochrome image to digital image processor card. The numerical analysis of the fringes images is done in many ways. The original programs for the analysis are presented.