An exemplary illuminating apparatus includes a light guiding plate, a light source facing a light input surface of the light guiding plate, and a complementary color element adjacent to the light source. The light source comprises a number of LEDs which emit light with at least two wavelengths. The at least two wavelengths light mix with each other to gain a white light. The complementary color element is configured for receiving light emitted from adjacent, outmost LED and converting the light into white light. The white light is reflected by the complementary color element and emits from the light guiding plate through the light output surface.