US Patent 7092092 Hand-carried LED polariscope

A polariscope that measures stress in glass and that is adapted to be hand-carried includes a lightweight, C-shaped housing with a sequential arrangement of a battery-powered LED light source, a first polarizer, a full wave plate at one distal end, and a second polarizer at a second distal end. The housing includes a hand-grip that houses a battery, where the battery is selectively connected to the LED light source with a switch carried on the hand-grip. The sequential arrangement of light source, first polarizer and full wave plate at the first distal end is less than two inches thick. The polariscope weighs less than two pounds and does not require an external power source.