**5.5 Luminous efficiency**

Three parameters reflect OLED's luminous performance: quantum efficiency, lighting quality and efficiency. Quantum performance can be split into internal quantum performance and external quantum performance [45]. The external quantum efficiency ηext corresponds to the proportion of photons (NP) released by the OLED in a given direction to the amount of injected (NC) electrons. OLED is a multilayer structure and the waveguide effect is responsible for absorbs or loses light. The inner quantum efficiency ηint corresponds to the real device's luminous effectiveness. The ratio of both reflects the ηC coefficient of optical coupling outside the apparatus in a certain direction.
