What is "leucoscope"

Leucoscope \Leu"co*scope\ (l[=u]"k[-o]*sk[=o]p), n. [Leuco- + -scope.] (Physics) An instrument, devised by Professor Helmholtz, for testing the color perception of the eye, or for comparing different lights, as to their constituent colors or their relative whiteness.

n. An instrument for testing the colour perception of the eye, or for comparing different lights in terms of their constituent colour or relative whiteness.