Over recent years, mean room surface exitance has gained acceptance as a predictor of perceived adequacy of illumination. However, it can be argued that mean room surface exitance either cannot be applied or has limited value in a number of practical situations. This paper proposes the use of a new metric, mean indirect cubic illuminance, to be used instead of mean room surface exitance in complex situations commonly found in practice. The paper also demonstrates that mean room surface exitance and average mean indirect cubic illuminance have nearly the same numerical values.