National Sleep Foundation: Lifetime Achievement Award Royal College of London: Adrian Gold Medal

[1] He is a leading researcher and author in the fields of the effects of light on human physiology, circadian rhythms and sleep medicine.

Czeisler investigates how the physiological system works to reset the human central circadian pacemaker, located in the hypothalamus and called the suprachiasmatic nucleus (SCN).

Czeisler then led the discovery that light transduced by non-visual input (melanopsin activation) could reset the circadian clock in patients without sight.

[20] Czeisler has also dedicated a portion of his career to examining the effects of light timing, duration, intensity, and wavelength on resetting the pacemaker through ipRGCs, which contain the photopigment melanopsin.

[19][13][21] He has also investigated the effects of chronic sleep deprivation and restriction, night shifts, and circadian disruption, on neurobehavioral performance and metabolism.

[7][13][21][22] Furthermore, Czeisler studied how sleep deprivation impairs the psychomotor performance of night shift workers (2009-2014),[19] specifically surgeons (2009-2013)[22] and residents (2010), police officers (2004-2008),[23] and truck drivers (2012).

Other research interests of his include studying wakefulness, sleep deprivation and how it can be prevented, and such influences on the clock as exercise and age.

[40] He instituted structural changes to the teams' schedules to allow for healthier sleep habits, including pushing morning practices into the afternoon and the '2 a.m. rule' which prevents players from traveling if they are going to arrive at their hotel later than 2:00 am.

In an interview with the Harvard Business Review, he explains that companies should seek to address this problem by setting behavioral expectations and scheduling policies for employees to avoid accruing sleep deficit.

[45] In 2018, Czeisler penned a powerful Perspective in The New England Journal of Medicine entitled "Housing Immigrant Children - The Inhumanity of Constant Illumination"[46] in which he harshly criticized the constant light exposure to which children were being subjected in detention centers while awaiting immigration processing, as this did not allow for exposure to light-dark cycles central to circadian regulation.

In 2023, together with Harvard Medical School Professor Elizabeth Klerman, Czeisler organized a seminar at the Harvard Radcliffe Institute to discuss whether daylight saving time should be eliminated or made permanent—a debate they call “another clash between scientific evidence and politics.” The seminar brought together researchers, policymakers, and members of the general public for a discussion.

The event was held in the Harvard Biological Laboratories, where Czeiser's colleagues, former pupils, friends, and family gathered to present plenary speeches and breakthrough scientific talks.