  The principal goal of this paper is to specify conditions of detection of
unresolved binaries by multicolor photometry. We have developed a method for
estimating the critical distance at which an unresolved binary of given mass
and age can be detected. The method is applied to the photometric system of the
planned Lyra-B spaceborne experiment. We have shown that some types of
unresolved binary stars can be discovered and distinguished from single stars
solely by means of photometric observations.
