The　luminous　efficacy　of　radiation　is　an　important　factor　influencing　to　the　luminous　efficiency　of　lighting.　White　LEDs　with　two　primary　colours　have　uncountable　metamerism　with　different　luminous　efficacy　of　radiation.　The　synthetic　range　of　the　white　LEDs　with　two　primary　colours　in　chromaticity　coordinate　is　determined　by　colour　matching　calculation,　and　the　selective　range　of　two　primary　colours　is　determined　to　obtain　high　luminous　efficacy　of　radiation　for　white　LEDs.