A dimmable circadian lighting system is provided that includes a light source and a control circuit in electrical communication with the light source and a dimmer. The control circuit is operative to vary a corelated color temperature (CCT) of the light source based on a signal from the dimmer; and maintain approximately a same lumen output of the light source across an upper transition zone of the dimmer extending from about 70% or greater of a range of the dimmer to about 100% of the range of the dimmer.