To provide a backlight device capable of satisfying various kinds of requests for colors and having a relatively simple configuration, and to provide its realization method.

This backlight device has a light source 410 providing first radiation and a phosphor, and has a filter layer 420 containing a optically coupled to the light source 410. The filter layer 420 is designed so as to absorb at least partially the first radiation, and to emit only one second radiation or a combined radiation of the first and second radiations. A light guide 430 designed so as to receive emitted light and reflect at least a part thereof is optically coupled to the filter layer 420. A display layer 440 is further optically coupled to the light guide 430.