A revised Kruithof graph based on empirical data

Kruithof’s graph identifies combinations of illuminance and correlated color temperature (CCT) alleged to yield pleasing visual conditions for interior lighting. Though in research terms the support provided by Kruithof is insufficient, it is widely cited as a design rule and has been the focus of many experimental studies despite evidence against Kruithof since at least 1990. The current article examines the trends displayed in those studies considered to provide credible evidence: these do not support Kruithof. For pleasant conditions, these data suggest only avoiding low illuminances and do not favor any CCT.